Fix bug in 1st pass motion compensation

In the case where the best reference mv is not (0,0) a secondary
search is carried out centered on (0,0). However, rather than
sending tmp_err into the search function, motion_error was
inadvertently passed.

As a result tmp_err remains set at INT_MAX and the (0,0)-based
search result will never be selected, even if it is better.

Change-Id: I3c82b246c8c82ba887b9d3fb4c9e0a0f2fe5a76c