linux-firmware: update Marvell PCIe-USB8997 firmware image

Firmware version for this image is 16.68.1.p140

In PCIe-USB chipset, WLAN is over PCIe whereas bluetooth is over
USB.

Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: James Cao <jcao@marvell.com>
Signed-off-by: Ganapathi Bhat <gbhat@marvell.com>