ext4: do not use yield()

Using yield() is strongly discouraged (see sched/core.c) especially
since we can just use cond_resched().

Replace all use of yield() with cond_resched().

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 117a9e7..48fc023 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1352,7 +1352,7 @@
 		ei->i_da_metadata_calc_last_lblock = save_last_lblock;
 		spin_unlock(&ei->i_block_reservation_lock);
 		if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
-			yield();
+			cond_resched();
 			goto repeat;
 		}
 		dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));