util: allocate larger tmp_row in util_format_translate

util: allocate larger tmp_row in util_format_translate

The tmp_row storage allocation took into account the format's y block
size by allocating y_step rows of data.  However, the x block size was
not being taken into account when deciding how wide those rows need to
be.

Now make sure that tmp_row is at least x_step by y_step in size.