Make DECLARE_ALIGNED_8 align to 8 bytes, never to 16

The DECLARE_ALIGNED_8 macro is defined to align to 16 bytes instead
the 8 suggested by the name on some CPUs.  None of the uses of this
macro ever need 16-byte alignment, cases which once did having been
changed to always specify 16 bytes explicitly.

Originally committed as revision 19737 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dsputil.h

@@ -640,7 +640,6 @@ void dsputil_init_pix_mmx(DSPContext* c, AVCodecContext *avctx);
 extern int mm_flags;
 
 #if HAVE_NEON
-#   define DECLARE_ALIGNED_8(t, v) DECLARE_ALIGNED(16, t, v)
 #   define STRIDE_ALIGN 16
 #endif
 
@@ -648,12 +647,10 @@ extern int mm_flags;
 
 extern int mm_flags;
 
-#define DECLARE_ALIGNED_8(t, v) DECLARE_ALIGNED(16, t, v)
 #define STRIDE_ALIGN 16
 
 #elif HAVE_MMI
 
-#define DECLARE_ALIGNED_8(t, v) DECLARE_ALIGNED(16, t, v)
 #define STRIDE_ALIGN 16
 
 #else
@@ -663,9 +660,7 @@ extern int mm_flags;
 
 #endif
 
-#ifndef DECLARE_ALIGNED_8
 #   define DECLARE_ALIGNED_8(t, v) DECLARE_ALIGNED(8, t, v)
-#endif
 
 #ifndef STRIDE_ALIGN
 #   define STRIDE_ALIGN 8