firmware: google: make structure gsmi_dev static

The structure gsmi_dev is local to the source and does not need to be
in global scope, so make it static.

Cleans up sparse warning:
symbol 'gsmi_dev' was not declared. Should it be static?

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>