Fix a bug in the C selfguided filter
Fix a bug in the C selfguided filter

Patch https://aomedia-review.googlesource.com/c/8321/ introduced
a bug in the C version of the self-guided filter in the case where
w = 384 and h > 368 or w > 368 and h = 384. This was due to forgetting
to adjust the offset between A and B in the C code.

This patch sets the offset correctly, resolving this bug.

Change-Id: I6bdf11aa76c37d0ecae02788b262e7a2e0a11a6e

luctrudeau/aom,GrokImageCompression/aom,smarter/aom,GrokImageCompression/aom,smarter/aom,luctrudeau/aom,GrokImageCompression/aom,GrokImageCompression/aom,luctrudeau/aom,luctrudeau/aom,GrokImageCompression/aom,luctrudeau/aom,smarter/aom,smarter/aom,GrokImageCompression/aom,smarter/aom,luctrudeau/aom,smarter/aom