icu: fix build after custom data library patch

Commit abded6bfead49d61c24a45d811a83ca082adf677 ("icu: add an option
to add a custom data library file") broke the build because of an
improper test on a non-qstripped variable. This commit fixes that.

Fixes:

  http://autobuild.buildroot.org/results/02a/02a0800b01a4bf8734d601f79dc12663fe8f7542/
  and many other similar occurences of the same issue.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/icu/icu.mk

@@ -26,9 +26,11 @@ ICU_MAKE = $(MAKE1)
 ICU_SUBDIR = source
 HOST_ICU_SUBDIR = source
 
-ifneq ($(BR2_PACKAGE_ICU_CUSTOM_DATA_PATH),)
+ICU_CUSTOM_DATA_PATH = $(call qstrip,$(BR2_PACKAGE_ICU_CUSTOM_DATA_PATH))
+
+ifneq ($(ICU_CUSTOM_DATA_PATH),)
 define ICU_COPY_CUSTOM_DATA
-	cp $(BR2_PACKAGE_ICU_CUSTOM_DATA_PATH) $(@D)/source/data/in/
+	cp $(ICU_CUSTOM_DATA_PATH) $(@D)/source/data/in/
 endef
 ICU_POST_PATCH_HOOKS += ICU_COPY_CUSTOM_DATA
 endif