MAINTAINERS: Switch a maintainer for drivers/staging/gasket

Todd Poynor takes over for John Joseph.

Signed-off-by: John Joseph <jnjoseph@google.com>
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>