Fix in initializing mi pointer grid at frame level
Fix in initializing mi pointer grid at frame level

MI pointer-grid/ mi-info in enc_setup_mi is memset accordingly to
handle super-resolution use case when size of current frame being
encoded is smaller than the previously coded frame.

Change-Id: I3280aa020bd4ec6436e3bacf5ccd3c742e93a3a8

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