[gdk-pixbuf] build: Fix typo in config.h comment

[Bastien Nocera <hadess src gnome org>]

commit a360c7ba234bbd4ca89744c898a14eece779e8e9
Author: Bastien Nocera <hadess hadess net>
Date:   Tue Aug 1 14:43:35 2017 +0100

    build: Fix typo in config.h comment

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 09e15ab..0db24b9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -759,7 +759,7 @@ if test $use_x86_asm = yes; then
     ac_ext=$save_ac_ext
     if test $use_mmx_asm = yes; then
       AC_DEFINE(USE_MMX, 1,
-                [Define to 1 if XXM is available and should be used])
+                [Define to 1 if MMX is available and should be used])
       AC_MSG_RESULT(yes)
     else
       AC_MSG_RESULT(no)