staging: rtl8723bs: Fix Coverity warning in rtw_dbg_port()

Fix the following Coverity warning:

File: drivers/staging/rtl8723bs/os_dep/ioctl_linux.c in function
rtw_dbg_port():

CID 18480: Operands don't affect result (CONSTANT_EXPRESSION_RESULT)
dead_error_condition: The condition (extra_arg & 7U) > 7U cannot be true.

        if ((extra_arg & 0x07) > 0x07)
                padapter->driver_ampdu_spacing = 0xFF;
        else
                padapter->driver_ampdu_spacing = extra_arg;

Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>