mt7601u: phy: Fix misnaming when documented function parameter 'dac'

mt7601u: phy: Fix misnaming when documented function parameter 'dac'

Fixes the following W=1 kernel build warning(s):

 drivers/net/wireless/mediatek/mt7601u/phy.c:1216: warning: Function parameter or member 'dac' not described in 'mt7601u_set_tx_dac'
 drivers/net/wireless/mediatek/mt7601u/phy.c:1216: warning: Excess function parameter 'path' description in 'mt7601u_set_tx_dac'

Cc: Jakub Kicinski <kubakici@wp.pl>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Felix Fietkau <nbd@openwrt.org>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: linux-mediatek@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Jakub Kicinski <kubakici@wp.pl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200819072402.3085022-16-lee.jones@linaro.org