ceph: propagate layout error on osd request creation

If we are creating an osd request and get an invalid layout, return
an EINVAL to the caller.  We switch up the return to have an error
code instead of NULL implying -ENOMEM.

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>

fs/ceph/addr.c

@@ -308,8 +308,8 @@ static int start_read(struct inode *inode, struct list_head *page_list, int max)
 				    NULL, 0,
 				    ci->i_truncate_seq, ci->i_truncate_size,
 				    NULL, false, 1, 0);
-	if (!req)
-		return -ENOMEM;
+	if (IS_ERR(req))
+		return PTR_ERR(req);
 
 	/* build page vector */
 	nr_pages = len >> PAGE_CACHE_SHIFT;
@@ -832,8 +832,8 @@ get_more_pages:
 					    ci->i_truncate_size,
 					    &inode->i_mtime, true, 1, 0);
 
-				if (!req) {
-					rc = -ENOMEM;
+				if (IS_ERR(req)) {
+					rc = PTR_ERR(req);
 					unlock_page(page);
 					break;
 				}