linux-firmware: allow LINUX_FIRMWARE_FILES to contain wildcards

This commit will allow the LINUX_FIRMWARE_FILES variable to contain
wildcards, which will simplify the handling of firmware that are
available in numerous revisions.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/linux-firmware/linux-firmware.mk

@@ -356,7 +356,8 @@ endif
 
 ifneq ($(LINUX_FIRMWARE_FILES),)
 define LINUX_FIRMWARE_INSTALL_FILES
-	$(TAR) c -C $(@D) $(sort $(LINUX_FIRMWARE_FILES)) | \
+	cd $(@D) ; \
+	$(TAR) c $(sort $(LINUX_FIRMWARE_FILES)) | \
 		$(TAR) x -C $(TARGET_DIR)/lib/firmware
 endef
 endif