staging: gasket: core: device register debug log cleanups

At device/driver registration time, convert a not-very-informative
info message to a more informative debug message, drop some not overly
helpful debug messages.

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