brcm80211: simplify assignment

Simplify assignment in wlc_phy_rxcal_gainctrl_nphy_rev5.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>