staging: gasket: fix multi-line comment syntax in gasket_core.h

Use consistent kernel-style multi-line comment syntax.

Reported-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Simon Que <sque@chromium.org>
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>