Only update skip when the tailing coeff num <= 2
Only update skip when the tailing coeff num <= 2

1) no need to update accu_dist in update_coeff_simple()
2) observe 0.09% coding gain on lowres limit=30

STATS_CHANGED

Change-Id: I6a7e1d0708e98ca8bb3a310eeec7ca6a7a0e3470

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