avcodec/alpha/me_cmp_alpha: Use proper me_cmp_func type

ea41e6d637 forgot
the int->ptrdiff_t switch for the stride. Libav didn't
do it because Libav had already dropped support for Alpha
at that point.
Only compilation has been tested for this commit.

(It might be that the ASM-versions of me_cmp_func functions
need to be updated as well.)

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/alpha/me_cmp_alpha.c

@@ -23,7 +23,8 @@
 #include "libavcodec/me_cmp.h"
 #include "asm.h"
 
-int pix_abs16x16_mvi_asm(void *v, const uint8_t *pix1, const uint8_t *pix2, int line_size, int h);
+int pix_abs16x16_mvi_asm(struct MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
+                         ptrdiff_t line_size, int h);
 
 static inline uint64_t avg2(uint64_t a, uint64_t b)
 {
@@ -44,7 +45,8 @@ static inline uint64_t avg4(uint64_t l1, uint64_t l2, uint64_t l3, uint64_t l4)
     return r1 + r2;
 }
 
-static int pix_abs8x8_mvi(void *v, const uint8_t *pix1, const uint8_t *pix2, int line_size, int h)
+static int pix_abs8x8_mvi(struct MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
+                          ptrdiff_t line_size, int h)
 {
     int result = 0;
 
@@ -119,7 +121,8 @@ int pix_abs16x16_mvi(const uint8_t *pix1, const uint8_t *pix2, int line_size)
 }
 #endif
 
-static int pix_abs16x16_x2_mvi(void *v, const uint8_t *pix1, const uint8_t *pix2, int line_size, int h)
+static int pix_abs16x16_x2_mvi(struct MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
+                               ptrdiff_t line_size, int h)
 {
     int result = 0;
     uint64_t disalign = (size_t) pix2 & 0x7;
@@ -192,7 +195,8 @@ static int pix_abs16x16_x2_mvi(void *v, const uint8_t *pix1, const uint8_t *pix2
     return result;
 }
 
-static int pix_abs16x16_y2_mvi(void *v, const uint8_t *pix1, const uint8_t *pix2, int line_size, int h)
+static int pix_abs16x16_y2_mvi(struct MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
+                               ptrdiff_t line_size, int h)
 {
     int result = 0;
 
@@ -245,7 +249,8 @@ static int pix_abs16x16_y2_mvi(void *v, const uint8_t *pix1, const uint8_t *pix2
     return result;
 }
 
-static int pix_abs16x16_xy2_mvi(void *v, const uint8_t *pix1, const uint8_t *pix2, int line_size, int h)
+static int pix_abs16x16_xy2_mvi(struct MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
+                                ptrdiff_t line_size, int h)
 {
     int result = 0;