brcmfmac: fix uninitialized warning

Building brcmfmac for sparc64 gave the following warning:

  CC [M]  drivers/net/wireless/brcm80211/brcmfmac/bcmsdh_sdmmc.o
    bcmsdh_sdmmc.c: In function 'brcmf_sdioh_request_byte':
     bcmsdh_sdmmc.c:89:6: warning: 'err_ret' may be used uninitialized
                          in this function [-Wuninitialized]

Inspecting the code it indeed had a path of execution in
which the return value was used uninitialized. This patch
fixes that code path.
Reviewed-by: NHante Meuleman <meuleman@broadcom.com>
Reviewed-by: NFranky Lin <frankyl@broadcom.com>
Reviewed-by: NPieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: NArend van Spriel <arend@broadcom.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

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

@@ -109,6 +109,8 @@ static inline int brcmf_sdioh_f0_write_byte(struct brcmf_sdio_dev *sdiodev,
 					brcmf_err("Disable F2 failed:%d\n",
 						  err_ret);
 			}
+		} else {
+			err_ret = -ENOENT;
 		}
 	} else if ((regaddr == SDIO_CCCR_ABORT) ||
 		   (regaddr == SDIO_CCCR_IENx)) {