i2c-bfin-twi: Fix mismatch in add timer and delete timer

Move init_completion to just before i2c transfer.
http://blackfin.uclinux.org/gf/project/uclinux-dist/tracker/?action=TrackerItemEdit&tracker_item_id=3385

Signed-off-by: Hans Schillstrom <hans.schillstrom@shlsys.com>
Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Jean Delvare <khali@linux-fr.org>