keys: Add Jarkko Sakkinen as co-maintainer

To address a major procedural concern on Linus's part the keyrings needs
a co-maintainer.
Suggested-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NJarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -9060,6 +9060,7 @@ F:	include/keys/trusted.h
 
 KEYS/KEYRINGS:
 M:	David Howells <dhowells@redhat.com>
+M:	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
 L:	keyrings@vger.kernel.org
 S:	Maintained
 F:	Documentation/security/keys/core.rst