vp8 mfqe: zero map[]

vp8 mfqe: zero map[]

The loop appears to set map[i] with the intention of running
the 'j' loop up to that point. However, without zero'ing map[]
first the behavior is unpredictable.

Fixes a static analysis warning:
warning: Branch condition evaluates to a garbage value
for (j = 0; j < 4 && map[j]; ++j) {

Change-Id: Ifa39353d8aa5cc47b467a7d3d8cdd3b5319fd997