drbd: don't cond_resched_lock with IRQs disabled

The last commit, drbd: add missing spinlock to bitmap receive,
introduced a cond_resched_lock(), where the lock in question is taken
with irqs disabled.

As we must not schedule with IRQs disabled,
and cond_resched_lock_irq() does not exist, yet,
we re-aquire the spin_lock_irq() for each bitmap page processed in turn.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_bitmap.c

@@ -1400,8 +1400,10 @@ void _drbd_bm_set_bits(struct drbd_conf *mdev, const unsigned long s, const unsi
 	/* first and full pages, unless first page == last page */
 	for (page_nr = first_page; page_nr < last_page; page_nr++) {
 		bm_set_full_words_within_one_page(mdev->bitmap, page_nr, first_word, last_word);
-		cond_resched_lock(&b->bm_lock);
+		spin_unlock_irq(&b->bm_lock);
+		cond_resched();
 		first_word = 0;
+		spin_lock_irq(&b->bm_lock);
 	}
 
 	/* last page (respectively only page, for first page == last page) */