swscale: [loongarch] Fix checkasm-sw_yuv2rgb failure.

Reviewed-by: 陈昊 <chenhao@loongson.cn>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 4713a5cc24)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswscale/loongarch/swscale_init_loongarch.c

@@ -93,6 +93,7 @@ av_cold SwsFunc ff_yuv2rgb_init_loongarch(SwsContext *c)
     int cpu_flags = av_get_cpu_flags();
 #if HAVE_LASX
     if (have_lasx(cpu_flags)) {
+        if (c->srcFormat == AV_PIX_FMT_YUV420P) {
             switch (c->dstFormat) {
                 case AV_PIX_FMT_RGB24:
                     return yuv420_rgb24_lasx;
@@ -120,8 +121,10 @@ av_cold SwsFunc ff_yuv2rgb_init_loongarch(SwsContext *c)
                         return yuv420_abgr32_lasx;
             }
         }
+    }
 #endif // #if HAVE_LASX
     if (have_lsx(cpu_flags)) {
+        if (c->srcFormat == AV_PIX_FMT_YUV420P) {
             switch (c->dstFormat) {
                 case AV_PIX_FMT_RGB24:
                     return yuv420_rgb24_lsx;
@@ -149,5 +152,6 @@ av_cold SwsFunc ff_yuv2rgb_init_loongarch(SwsContext *c)
                         return yuv420_abgr32_lsx;
             }
         }
+    }
     return NULL;
 }

libswscale/loongarch/yuv2rgb_lasx.c

@@ -82,8 +82,8 @@
 #define YUV2RGB_RES                                                        \
     m_y1 = __lasx_xvldrepl_d(py_1, 0);                       \
     m_y2 = __lasx_xvldrepl_d(py_2, 0);                       \
-    m_u  = __lasx_xvldrepl_d(pu, 0);                         \
-    m_v  = __lasx_xvldrepl_d(pv, 0);                         \
+    m_u  = __lasx_xvldrepl_w(pu, 0);                         \
+    m_v  = __lasx_xvldrepl_w(pv, 0);                         \
     m_y1 = __lasx_xvilvl_d(m_y2, m_y1);                      \
     m_u  = __lasx_xvilvl_b(m_u, m_u);                        \
     m_v  = __lasx_xvilvl_b(m_v, m_v);                        \