Use proper inttypes for varaiance computations
Use proper inttypes for varaiance computations

This commit correct the integer types used in variance functions. It
now uses same integer type when number of pixels are same, e.g
16x64 and 64x16 use same integer types as 32x32
8x32 and 32x8 use same integer types as 16x16

Change-Id: I1a54ba8d73e09126e680ae5af3ee52395a41df41

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom