bcache: Really show state of work pending bit

bcache: Really show state of work pending bit

WORK_STRUCT_PENDING is a mask for testing the pending bit.
test_bit() expects the number of the bit and we need to
use WORK_STRUCT_PENDING_BIT there.

Also work_data_bits() is defined in workqueues.h now.

I have noticed this just by chance when looking how
WORK_STRUCT_PENDING_BIT is used. The change is compile
tested.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>