certs: Fix misaligned data in extra certificate list

Fix the following warning found by kbuild:

	certs/system_certificates.S:24: Error: misaligned data

because:

	KEYS: Reserve an extra certificate symbol for inserting without recompiling

doesn't correctly align system_extra_cert_used.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Mehmet Kayaalp <mkayaalp@linux.vnet.ibm.com>

certs/system_certificates.S

@@ -19,6 +19,7 @@ __cert_list_end:
 VMLINUX_SYMBOL(system_extra_cert):
 	.fill CONFIG_SYSTEM_EXTRA_CERTIFICATE_SIZE, 1, 0
 
+	.align 4
 	.globl VMLINUX_SYMBOL(system_extra_cert_used)
 VMLINUX_SYMBOL(system_extra_cert_used):
 	.int 0