jbd2: simplify error path on allocation failure in do_get_write_access()

We were acquiring bh_state_lock when allocation of buffer failed in
do_get_write_access() only to be able to jump to a label that releases
the lock and does all other checks that don't make sense for this error
path. Just jump into the right label instead.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>