Fix spelling mistake: partiton => partition.
Fix spelling mistake: partiton => partition.

Reported by jcowgill@jcowgill.uk.

BUG=aomedia:2089

Change-Id: I2abcc1cadfa0f96ad1bba0807618116fdba3a18c

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