wifi: wcn36xx: main: fix sparse warnings

Sparse warns:

drivers/net/wireless/ath/wcn36xx/main.c:758:58: warning: incorrect type in assignment (different base types)
drivers/net/wireless/ath/wcn36xx/main.c:758:58:    expected unsigned short [usertype] vht_rx_mcs_map
drivers/net/wireless/ath/wcn36xx/main.c:758:58:    got restricted __le16 [usertype] rx_mcs_map
drivers/net/wireless/ath/wcn36xx/main.c:760:58: warning: incorrect type in assignment (different base types)
drivers/net/wireless/ath/wcn36xx/main.c:760:58:    expected unsigned short [usertype] vht_tx_mcs_map
drivers/net/wireless/ath/wcn36xx/main.c:760:58:    got restricted __le16 [usertype] tx_mcs_map

le16_to_cpu() was just missing. Compile tested only.

Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240320182449.3757215-4-kvalo@kernel.org