mt76: mt7915: fix endian issues

Multiple MCU messages were using u16/u32 fields without endian annotations
or conversions

Fixes: e57b7901 ("mt76: add mac80211 driver for MT7915 PCIe-based chipsets")
Fixes: 5517f78b

 ("mt76: mt7915: enable firmware module debug support")
Signed-off-by: Felix Fietkau <nbd@nbd.name>