brcmfmac: avoid gcc-5.1 warning

gcc-5.0 gained a new warning in the fwsignal portion of the brcmfmac
driver:

drivers/net/wireless/brcm80211/brcmfmac/fwsignal.c: In function 'brcmf_fws_txs_process':
drivers/net/wireless/brcm80211/brcmfmac/fwsignal.c:1478:8: warning: 'skb' may be used uninitialized in this function [-Wmaybe-uninitialized]

This is a false positive, and marking the brcmf_fws_hanger_poppkt function
as 'static inline' makes the warning go away. I have checked the object
file output and while a little code gets moved around, the size of
the binary remains identical.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/brcm80211/brcmfmac/fwsignal.c

@@ -635,7 +635,7 @@ static int brcmf_fws_hanger_pushpkt(struct brcmf_fws_hanger *h,
 	return 0;
 }
 
-static int brcmf_fws_hanger_poppkt(struct brcmf_fws_hanger *h,
+static inline int brcmf_fws_hanger_poppkt(struct brcmf_fws_hanger *h,
 					  u32 slot_id, struct sk_buff **pktout,
 					  bool remove_item)
 {