copy compiler warning fixes

generic version got fixed, but not the arm version. fixes:
vp8/encoder/arm/mcomp_arm.c: In function 'vp8_full_search_sadx3':
vp8/encoder/arm/mcomp_arm.c:1208: warning: pointer targets in passing
argument 5 of 'fn_ptr->sdx3f' differ in signedness
vp8/encoder/arm/mcomp_arm.c:1208: note: expected 'unsigned int *' but
argument is of type 'int *'

and another unsigned change to keep the files similar

Change-Id: I1b6255dc3a03b90394a791ee0d15d8167d9454db