Bluetooth: hci_bcm: Use default baud rate if missing shutdown GPIO

In case the shutdown GPIO is not wired up, it is impossible to reset the
Bluetooth controller to its original state. This include the initial
default baud rate which leads to issues when reloading the module or
when something unexpected happens. To avoid any kind of runtime
deadlocks, stick with the initial default baud rate.

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