lavc/idctdsp: improve R-V V put_signed_pixels_clamped

This follows the same idea as with pixblockdsp, but applied at the
other end, whilst writing data at the end of the function.

libavcodec/riscv/idctdsp_rvv.S

@@ -42,24 +42,15 @@ func ff_put_pixels_clamped_rvv, zve32x
         ret
 endfunc
 
-func ff_put_signed_pixels_clamped_rvv, zve32x
-        vsetivli    zero, 8, e16, m1, ta, ma
-        vlseg8e16.v v24, (a0)
-
-        li          t1, 128
-        vsetivli    zero, 8, e8, mf2, ta, ma
-        vnclip.wi   v16, v24, 0
-        vnclip.wi   v17, v25, 0
-        vnclip.wi   v18, v26, 0
-        vnclip.wi   v19, v27, 0
-        vnclip.wi   v20, v28, 0
-        vnclip.wi   v21, v29, 0
-        vnclip.wi   v22, v30, 0
-        vnclip.wi   v23, v31, 0
-        vsetvli     t0, zero, e8, m8, ta, ma
-        vadd.vx     v16, v16, t1
-        vsetivli    zero, 8, e8, mf2, ta, ma
-        vssseg8e8.v v16, (a1), a2
+func ff_put_signed_pixels_clamped_rvv, zve64x
+        li      t0, 8 * 8
+        vsetvli zero, t0, e8, m4, ta, ma
+        vle16.v v24, (a0)
+        li      t1, 128
+        vnclip.wi v16, v24, 0
+        vadd.vx v16, v16, t1
+        vsetivli zero, 8, e8, mf2, ta, ma
+        vsse64.v v16, (a1), a2
         ret
 endfunc