libceph, ceph: change ceph_calc_file_object_mapping() signature

- make it void
- xlen (object extent length) out parameter should be u32 because only
  a single stripe unit is mapped at a time

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index b4336b4..c0fe1b6 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -945,19 +945,15 @@
 			if (locked_pages == 0) {
 				u64 objnum;
 				u64 objoff;
+				u32 xlen;
 
 				/* prepare async write request */
 				offset = (u64)page_offset(page);
-				len = wsize;
-
-				rc = ceph_calc_file_object_mapping(&ci->i_layout,
-								offset, len,
-								&objnum, &objoff,
-								&len);
-				if (rc < 0) {
-					unlock_page(page);
-					break;
-				}
+				ceph_calc_file_object_mapping(&ci->i_layout,
+							      offset, wsize,
+							      &objnum, &objoff,
+							      &xlen);
+				len = xlen;
 
 				num_ops = 1;
 				strip_unit_end = page->index +