brcmfmac: remove set but not used variables 'sfdoff' and 'pad_size'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c: In function 'brcmf_sdio_rxglom':
drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c:1466:11: warning:
 variable 'sfdoff' set but not used [-Wunused-but-set-variable]

drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c: In function 'brcmf_sdio_bus_preinit':
drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c:3408:7: warning:
 variable 'pad_size' set but not used [-Wunused-but-set-variable]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>