mt76: mt7615: fix sparse warnings: warning: cast from restricted __le16

mt76: mt7615: fix sparse warnings: warning: cast from restricted __le16

Do not convert {tx,rx}_mcs_map to little-endian since it is already done
by mac80211. This patch fix the following sparse warning:

drivers/net/wireless/mediatek/mt76/mt7615/mcu.c:1497:25: sparse:
warning: cast from restricted __le16
drivers/net/wireless/mediatek/mt76/mt7615/mcu.c:1499:25: sparse:
warning: cast from restricted __le16

Fixes: 04b8e65922f6 ("mt76: add mac80211 driver for MT7615 PCIe-based chipsets")
Fixes: 3ca0a6f6e9df ("mt7615: mcu: use standard signature for mt7615_mcu_msg_send")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>