x86/vf_hflip: don't load the width argument twice

Signed-off-by: James Almer <jamrial@gmail.com>

libavfilter/x86/vf_hflip.asm

@@ -33,7 +33,7 @@ INIT_XMM ssse3
 cglobal hflip_byte, 3, 5, 3, src, dst, w, r, x
     mova    m0, [pb_flip_byte]
     mov     xq, 0
-    mov     wd, dword wm
+    movsxdifnidn wq, wd
     mov     rq, wq
     and     rq, 2 * mmsize - 1
     cmp     wq, 2 * mmsize
@@ -71,8 +71,7 @@ RET
 cglobal hflip_short, 3, 5, 3, src, dst, w, r, x
     mova    m0, [pb_flip_short]
     mov     xq, 0
-    mov     wd, dword wm
-    add     wq, wq
+    add     wd, wd
     mov     rq, wq
     and     rq, 2 * mmsize - 1
     cmp     wq, 2 * mmsize