package/gcc: fix xtensa overlay for gcc ccache hash

Commit b3b60706221d (arch/xtensa: allow specifying path to tarball file)
missed a place where the xtensa overlay was referenced, thus breaking
the calculation for the ccache hash.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/gcc/gcc.mk

@@ -283,7 +283,7 @@ HOST_GCC_COMMON_CCACHE_HASH_FILES += \
 		$(addsuffix /gcc/$(GCC_VERSION)/*.patch,$(call qstrip,$(BR2_GLOBAL_PATCH_DIR))) \
 		$(addsuffix /gcc/*.patch,$(call qstrip,$(BR2_GLOBAL_PATCH_DIR)))))
 ifeq ($(BR2_xtensa),y)
-HOST_GCC_COMMON_CCACHE_HASH_FILES += $(ARCH_XTENSA_OVERLAY_TAR)
+HOST_GCC_COMMON_CCACHE_HASH_FILES += $(ARCH_XTENSA_OVERLAY_FILE)
 endif
 
 # _CONF_OPTS contains some references to the absolute path of $(HOST_DIR)