mt7615: mcu: remove bss_info_convert_vif_type routine

Remove bss_info_convert_vif_type routine since it is run just in
mt7615_mcu_set_bss_info and the switch over vif->type is already there.
Simplify mt7615_mcu_set_bss_info routine

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>