[CIFS] Fix warnings shown by newer version of sparse

Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/link.c b/fs/cifs/link.c
index 6a85ef7..11f2657 100644
--- a/fs/cifs/link.c
+++ b/fs/cifs/link.c
@@ -237,7 +237,7 @@
 	char *tmp_path = NULL;
 	char *tmpbuffer;
 	unsigned char *referrals = NULL;
-	int num_referrals = 0;
+	unsigned int num_referrals = 0;
 	int len;
 	__u16 fid;