u-boot: fix custom patch dir handling

Signed-off-by: Ossy <ossy1980@gmx.net>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

boot/u-boot/u-boot.mk

@@ -77,8 +77,8 @@ $(U_BOOT_DIR)/.patched: $(U_BOOT_DIR)/.unpacked
 	toolchain/patch-kernel.sh $(U_BOOT_DIR) boot/u-boot \
 		u-boot-$(U_BOOT_VERSION)-\*.patch \
 		u-boot-$(U_BOOT_VERSION)-\*.patch.$(ARCH)
-ifneq ($(qstrip $(BR2_TARGET_UBOOT_CUSTOM_PATCH_DIR)),)
-	toolchain/patch-kernel.sh $(U_BOOT_DIR) $(U_BOOT_CUSTOM_PATCH_DIR) u-boot-$(U_BOOT_VERSION)-\*.patch
+ifneq ($(strip $(BR2_TARGET_UBOOT_CUSTOM_PATCH_DIR)),"")
+	toolchain/patch-kernel.sh $(U_BOOT_DIR) $(BR2_TARGET_UBOOT_CUSTOM_PATCH_DIR) u-boot-$(U_BOOT_VERSION)-\*.patch
 endif
 	touch $@