valgrind: fix build failure on uml

Signed-off-by: Nicolas Thill <nico@openwrt.org>

SVN-Revision: 42229

package/devel/valgrind/Makefile

@@ -77,7 +77,7 @@ define Package/valgrind/description
 	to speed up and reduce memory use of your programs.
 endef
 
-CPU := $(patsubst x86_64,amd64,$(patsubst x86,i386,$(LINUX_KARCH)))
+CPU := $(patsubst x86_64,amd64,$(patsubst x86,i386,$(patsubst um,$(ARCH),$(LINUX_KARCH))))
 
 CONFIGURE_VARS += \
 	UNAME_R=$(LINUX_VERSION)