Bluetooth: hci_ll: Add endianness conversion when setting baudrate

This adds an endianness conversion when setting the baudrate using a
vendor-specific command. Otherwise, bad things might happen on a big-
endian system.

Suggested-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>