certs: Fix build error when CONFIG_MODULE_SIG_KEY is PKCS#11 URI

When CONFIG_MODULE_SIG_KEY is PKCS#11 URL (pkcs11:*), signing_key.x509
fails to build:

  certs/Makefile:77: *** target pattern contains no '%'.  Stop.

Due to the typo, $(X509_DEP) contains a colon.

Fix it.

Fixes: b8c96a6b ("certs: simplify $(srctree)/ handling and remove config_filename macro")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

certs/Makefile

@@ -68,7 +68,7 @@ $(obj)/x509.genkey:
 endif # CONFIG_MODULE_SIG_KEY
 
 # If CONFIG_MODULE_SIG_KEY isn't a PKCS#11 URI, depend on it
-ifneq ($(filter-out pkcs11:%, %(CONFIG_MODULE_SIG_KEY)),)
+ifneq ($(filter-out pkcs11:%, $(CONFIG_MODULE_SIG_KEY)),)
 X509_DEP := $(CONFIG_MODULE_SIG_KEY)
 endif