certs: Fix build error when PKCS#11 URI contains semicolon

When CONFIG_MODULE_SIG_KEY is PKCS#11 URI (pkcs11:*) and contains a
semicolon, signing_key.x509 fails to build:

  certs/extract-cert pkcs11:token=foo;object=bar;pin-value=1111 certs/signing_key.x509
  Usage: extract-cert <source> <dest>

Add quotes to the extract-cert argument to avoid splitting by the shell.

This approach was suggested by Masahiro Yamada <masahiroy@kernel.org>.

Fixes: 129ab0d2 ("kbuild: do not quote string values in include/config/auto.conf")
Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

certs/Makefile

@@ -23,8 +23,8 @@ $(obj)/blacklist_hash_list: $(CONFIG_SYSTEM_BLACKLIST_HASH_LIST) FORCE
 targets += blacklist_hash_list
 
 quiet_cmd_extract_certs  = CERT    $@
-      cmd_extract_certs  = $(obj)/extract-cert $(extract-cert-in) $@
-extract-cert-in = $(or $(filter-out $(obj)/extract-cert, $(real-prereqs)),"")
+      cmd_extract_certs  = $(obj)/extract-cert "$(extract-cert-in)" $@
+extract-cert-in = $(filter-out $(obj)/extract-cert, $(real-prereqs))
 
 $(obj)/system_certificates.o: $(obj)/x509_certificate_list