drivers_base: make argument to platform_device_register_full const

platform_device_register_full doesn't modify *pdevinfo so it can be
marked as const without further adaptions.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>