avcodec/x86/vp6dsp: Don't align the stack manually

For most systems (particularly all x64), the stack is already
guaranteed to be sufficiently aligned. So just use x86inc's
stack feature which does the right thing.

Reviewed-by: Lynne <dev@lynne.ee>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/x86/vp6dsp.asm

@@ -62,11 +62,7 @@ SECTION .text
 ; void ff_vp6_filter_diag4_<opt>(uint8_t *dst, uint8_t *src, ptrdiff_t stride,
 ;                                const int16_t h_weight[4], const int16_t v_weights[4])
 INIT_XMM sse2
-cglobal vp6_filter_diag4, 5, 7, 8
-    mov          r5, rsp         ; backup stack pointer
-    and         rsp, ~(mmsize-1) ; align stack
-    sub         rsp, 8*11
-
+cglobal vp6_filter_diag4, 5, 6, 8, -8*11
     sub          r1, r2
 
     pxor         m7, m7
@@ -74,25 +70,24 @@ cglobal vp6_filter_diag4, 5, 7, 8
     SPLAT4REGS
 
     mov          r3, rsp
-    mov          r6, 11
+    mov         r5d, 11
 .nextrow:
     DIAG4        r1, -1, 0, 1, 2, r3
     add          r3, 8
     add          r1, r2
-    dec          r6
+    dec         r5d
     jnz .nextrow
 
     movq         m3, [r4]
     SPLAT4REGS
 
     lea          r3, [rsp+8]
-    mov          r6, 8
+    mov         r1d, 8
 .nextcol:
     DIAG4        r3, -8, 0, 8, 16, r0
     add          r3, 8
     add          r0, r2
-    dec          r6
+    dec         r1d
     jnz .nextcol
 
-    mov         rsp, r5          ; restore stack pointer
     RET