firmware: dvb/dvb-usb: prepare for FIRMWARE_NAME_MAX removal

We're going to remove the FIRMWARE_NAME_MAX definition in order to avoid any
firmware name length restriction.
This patch changes the dvb_usb_device_properties firmware field accordingly.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Reviewed-by: Michael Krufky <mkrufky@kernellabs.com>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>