Bluetooth: Fix sparse warning with btmrvl driver

This patch fixes the following sparse warning caused by a missing
declaration in the header file:

drivers/bluetooth/btmrvl_main.c:218:5: warning: symbol 'btmrvl_pscan_window_reporting' was not declared. Should it be static?

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>