nasm: end labels with colon (':')

Labels should end by colon (':'), nasm requires it.

Provide nasm compatibility.  No binary change by this patch with yasm
on {x86_64,i686}-fedora13-linux-gnu.  Few longer opcodes with nasm on
{x86_64,i686}-fedora13-linux-gnu have been checked as safe.

Change-Id: I0b2ec6f01afb061d92841887affb5ca0084f936f

vp8/encoder/x86/subtract_mmx.asm

diff --git a/vp8/encoder/x86/subtract_mmx.asm b/vp8/encoder/x86/subtract_mmx.asm
index 5775d98..c381ffd 100644
--- a/vp8/encoder/x86/subtract_mmx.asm
+++ b/vp8/encoder/x86/subtract_mmx.asm
@@ -15,7 +15,7 @@
 ;                            unsigned short *diff, unsigned char *Predictor,
 ;                            int pitch);
 global sym(vp8_subtract_b_mmx_impl)
-sym(vp8_subtract_b_mmx_impl)
+sym(vp8_subtract_b_mmx_impl):
     push        rbp
     mov         rbp, rsp
     SHADOW_ARGS_TO_STACK 5
@@ -151,7 +151,7 @@
 
 ;void vp8_subtract_mbuv_mmx(short *diff, unsigned char *usrc, unsigned char *vsrc, unsigned char *pred, int stride)
 global sym(vp8_subtract_mbuv_mmx)
-sym(vp8_subtract_mbuv_mmx)
+sym(vp8_subtract_mbuv_mmx):
     push        rbp
     mov         rbp, rsp
     SHADOW_ARGS_TO_STACK 5