wimax/i2400m: driver defaults to firmware v1.5 for i5x50 devices

Updates the i2400m driver to default to firmware versions v1.5 for the
Intel Wireless WiMAX Connection 5150 and 5350 devices.

Firmware available in linux-firmware.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>