openrisc: use generic strnlen_user() function

The generic version is both easier to support and more correct.

Signed-off-by: Jonas Bonn <jonas@southpole.se>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index 0656232..49765b5 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -20,6 +20,7 @@
 	select GENERIC_ATOMIC64
 	select GENERIC_CLOCKEVENTS
 	select GENERIC_STRNCPY_FROM_USER
+	select GENERIC_STRNLEN_USER
 
 config MMU
 	def_bool y