firmware: wireless/libertas: 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 eplaces the shared FIRMWARE_NAME_MAX definition with a libertas
local one.

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Acked-by: Dan Williams <dcbw@redhat.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>