staging: rtl8192su: fix a compiler warning

fix for:
drivers/staging/rtl8192su/r8192U_core.c: In function ‘rtl8192SU_MacConfigAfterFwDownload’:
drivers/staging/rtl8192su/r8192U_core.c:4403:24: warning: comparison between ‘rtl819xUsb_loopback_e’ and ‘enum _RTL8192SUSB_LOOPBACK’
drivers/staging/rtl8192su/r8192U_core.c:4405:30: warning: comparison between ‘rtl819xUsb_loopback_e’ and ‘enum _RTL8192SUSB_LOOPBACK’

Signed-off-by: Florian Schilhabel <florian.c.schilhabel@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>