staging: rtl8723bs: Fix potential usage while NULL error in hal/rtl8723b_hal_init.c

Smatch logs the following:

  CHECK   drivers/staging/rtl8723bs/hal/rtl8723b_hal_init.c
drivers/staging/rtl8723bs/hal/rtl8723b_hal_init.c:518 rtl8723b_FirmwareDownload() error: we previously assumed 'pFirmware' could be null (see line 382)

Fixing this error required a rewrite of the error exits from this routine.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>