PKCS#7: fix sparse non static symbol warning

Fixes the following sparse warnings:

crypto/asymmetric_keys/pkcs7_key_type.c:73:17: warning:
 symbol 'key_type_pkcs7' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: David Howells <dhowells@redhat.com>

crypto/asymmetric_keys/pkcs7_key_type.c

@@ -70,7 +70,7 @@ error:
  * user defined keys take an arbitrary string as the description and an
  * arbitrary blob of data as the payload
  */
-struct key_type key_type_pkcs7 = {
+static struct key_type key_type_pkcs7 = {
 	.name			= "pkcs7_test",
 	.def_lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
 	.preparse		= pkcs7_preparse,