pkg-infra: fix missing 3993 for AUTOTARGET's SUBDIR

Ensure <pkg>_SUBDIR gets resolved late, so that E.G. the default values
for host packages are taken into consideration.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/Makefile.autotools.in

@@ -93,7 +93,7 @@ $(2)_CLEAN_OPT			?= clean
 $(2)_UNINSTALL_STAGING_OPT	?= DESTDIR=$$(STAGING_DIR) uninstall
 $(2)_UNINSTALL_TARGET_OPT	?= DESTDIR=$$(TARGET_DIR)  uninstall
 
-$(2)_SRCDIR                     = $$($(2)_DIR)/$($(2)_SUBDIR)
+$(2)_SRCDIR                     = $$($(2)_DIR)/$$($(2)_SUBDIR)
 
 #
 # Configure step. Only define it if not already defined by the package