Harmonize declarations in loopfilter.[hc]
Harmonize declarations in loopfilter.[hc]

This was causing build warnings on Visual Studio due to 'const'
mismatch.

BUG=aomedia:442

Change-Id: Id7089c332c0f973d4d9eeff3296f5dbc2bcbd374

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