Driver core: switch firmware_class to uevent_suppress.

Use uevent_suppress instead of returning an error code in
firmware_uevent(). Get rid of the now unneeded FW_STATUS_READY
and FW_STATUS_READY_NOHOTPLUG.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>