Bluetooth: hci_bcm: Fix unwanted error reporting if no bcm dev

The hci_bcm proto is able to operate without bcm platform device linked
to its uart port. In that case, firmware can be applied, but there is
no power operation (no gpio/irq resources mgmt).

However, the current implementation breaks this use case because of
reporting a ENODEV error in the bcm setup procedure if bcm_request_irq
fails (which is the case if no bcm device linked).

Fix this by removing bcm_request_irq error forwarding.

Signed-off-by: Loic Poulain <loic.poulain@intel.com>
Reported-by: Ian Molton <ian@mnementh.co.uk>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>