wifi: brcmfmac: Add brcmf_c_set_cur_etheraddr() helper

Add a little helper to send "cur_etheraddr" commands to the interface
and to handle the error reporting of it in a single place.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Arend van Spriel <aspriel@gmail.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220708133712.102179-1-hdegoede@redhat.com