Remove useless alignment from MpegEncContext.intra_scantable

The first member of struct ScanTable is a simple pointer, extra alignment
of which serves no purpose.  The alignment specifier was added along with
some Altivec optimisations also adding a 16-byte-aligned array at the end
of struct ScanTable.  Presumably the redundant, outer alignment was added
by mistake.  The inner one is clearly sufficient.

Originally committed as revision 19724 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo.h

@@ -436,7 +436,7 @@ typedef struct MpegEncContext {
     uint16_t (*q_inter_matrix16)[2][64];
     int block_last_index[12];  ///< last non zero coefficient in block
     /* scantables */
-    DECLARE_ALIGNED_8(ScanTable, intra_scantable);
+    ScanTable intra_scantable;
     ScanTable intra_h_scantable;
     ScanTable intra_v_scantable;
     ScanTable inter_scantable; ///< if inter == intra then intra should be used to reduce tha cache usage