staging: brcm80211: fixed error in non-DHD_DEBUG fullmac build

A build error was introduced with recent fullmac changes when building without
debug option configured:

drivers/staging/brcm80211/brcmfmac/dhd_sdio.c: In function
  ‘dhdsdio_sdiod_drive_strength_init’:
drivers/staging/brcm80211/brcmfmac/dhd_sdio.c:6366:3: error: ‘chn’ undeclared

Cc: devel@linuxdriverproject.org
Cc: linux-wireless@vger.kernel.org
Cc: Brett Rudley <brudley@broadcom.com>
Cc: Henry Ptasinski <henryp@broadcom.com>
Cc: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/brcm80211/brcmfmac/dhd_sdio.c

@@ -6338,9 +6338,7 @@ dhdsdio_sdiod_drive_strength_init(struct dhd_bus *bus, u32 drivestrength) {
 	struct sdiod_drive_str *str_tab = NULL;
 	u32 str_mask = 0;
 	u32 str_shift = 0;
-#ifdef BCMDBG
 	char chn[8];
-#endif
 
 	if (!(bus->ci->cccaps & CC_CAP_PMU))
 		return;