rdopt: clear maybe-uninitialized variable warning

av1/encoder/rdopt.c:9533 ‘zeromv[1].as_int’ may be used
uninitialized in this function [-Wmaybe-uninitialized]
this was spurious given the logic in the if

Change-Id: I8ddfe7e46d1bf5593cc8624f05c9f181243a87d4
1 file changed