mt76: mt7915: fix sparse warnings: incorrect type initializer

drivers/net/wireless/mediatek/mt76/mt7915/mcu.c:2317:31: sparse: sparse:
incorrect type in initializer (different base types)

Fixes: 5517f78b ("mt76: mt7915: enable firmware module debug support")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>