brcmfmac: btcoex: replace init_timer with setup_timer

setup_timer.cocci suggested the following improvement:
drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c:383:1-11: Use
setup_timer function for function on line 384.

The combination of init_timer and setting up the data and function field
manually is equivalent to calling setup_timer(). This is an api
consolidation only and improves readability.

Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Xie Qirong <cheerx1994@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>