um: Fix return value of strnlen_user()

In case of an error it must not return -EFAULT.
Return 0 like all other archs do.

Reported-by: toralf.foerster@gmx.de
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/kernel/skas/uaccess.c b/arch/um/kernel/skas/uaccess.c
index 1d3e0c1..4ffb644 100644
--- a/arch/um/kernel/skas/uaccess.c
+++ b/arch/um/kernel/skas/uaccess.c
@@ -254,6 +254,6 @@
 	n = buffer_op((unsigned long) str, len, 0, strnlen_chunk, &count);
 	if (n == 0)
 		return count + 1;
-	return -EFAULT;
+	return 0;
 }
 EXPORT_SYMBOL(strnlen_user);