btrfs: replace remaining do_div calls with div_u64 variants

Switch to div_u64_rem that does type checking and has more obvious
semantics than do_div.

Signed-off-by: David Sterba <dsterba@suse.cz>
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 13c9b46..764528a 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -1673,7 +1673,7 @@
 		 */
 		if (*bytes >= align) {
 			tmp = entry->offset - ctl->start + align - 1;
-			do_div(tmp, align);
+			tmp = div64_u64(tmp, align);
 			tmp = tmp * align + ctl->start;
 			align_off = tmp - entry->offset;
 		} else {