ceph: adjust 36 checks for NULL pointers

The script “checkpatch.pl” pointed information out like the following.

Comparison to NULL could be written ...

Thus fix the affected source code places.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Yan, Zheng <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 9634eb7..65a6fa1 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -175,7 +175,7 @@ static int ceph_init_file(struct inode *inode, struct file *file, int fmode)
 		dout("init_file %p %p 0%o (regular)\n", inode, file,
 		     inode->i_mode);
 		cf = kmem_cache_zalloc(ceph_file_cachep, GFP_KERNEL);
-		if (cf == NULL) {
+		if (!cf) {
 			ceph_put_fmode(ceph_inode(inode), fmode); /* clean up */
 			return -ENOMEM;
 		}