vp9_bilinear_filters_mmx: add missing extern specifiers

Change-Id: Ibabf18947f90cb4f45052763ebf44cfb8209bd8b

vp9/encoder/x86/vp9_variance_mmx.c

@@ -191,7 +191,7 @@ unsigned int vp9_variance8x16_mmx(
 
 }
 
-DECLARE_ALIGNED(16, const short, vp9_bilinear_filters_mmx[16][8]);
+DECLARE_ALIGNED(16, extern const short, vp9_bilinear_filters_mmx[16][8]);
 
 unsigned int vp9_sub_pixel_variance4x4_mmx
 (

vp9/encoder/x86/vp9_variance_sse2.c

@@ -137,7 +137,7 @@ void vp9_half_vert_variance16x_h_sse2
   unsigned int *sumsquared
 );
 
-DECLARE_ALIGNED(16, extern short, vp9_bilinear_filters_mmx[16][8]);
+DECLARE_ALIGNED(16, extern const short, vp9_bilinear_filters_mmx[16][8]);
 
 unsigned int vp9_variance4x4_wmt(
   const unsigned char *src_ptr,