warped_motion.h: correct warped_motion definition
warped_motion.h: correct warped_motion definition

should be marked extern as the table is defined in warped_motion.c.
prevents multiple common symbol definitions and link warnings for table
size change between e.g., encoder.c and warped_motion.c.

Change-Id: Ic709497d7cd2020fde0167201f696916ce220f54

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