gst/mpegstream/gstmpegparse.c: Use our alignment-safe macros here too, since we can...

gst/mpegstream/gstmpegparse.c: Use our alignment-safe macros here too, since we can't assume that

Original commit message from CVS:
* gst/mpegstream/gstmpegparse.c: (gst_mpeg_parse_parse_packhead):
Use our alignment-safe macros here too, since we can't assume that
GST_BUFFER_DATA is aligned (these are subbuffers we're dealing with
here).