sanitize const/signedness for udf

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index f90231e..378a759 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -1672,7 +1672,7 @@
 		return -1;
 
 	if (epos->offset + (2 * adsize) > inode->i_sb->s_blocksize) {
-		char *sptr, *dptr;
+		unsigned char *sptr, *dptr;
 		struct buffer_head *nbh;
 		int err, loffset;
 		struct kernel_lb_addr obloc = epos->block;