rtlwifi: avoid accessing RCR directly

The rtl*_set_check_bssid functions are mostly the same, but access the
RCR register in different ways. Use the get_hw_reg abstraction layer
(which reads rtlpci->receive_config for PCI devices and mac->rx_conf for
USB).

There is no functional change for cases where receive_config was
accessed directly. For rtl8192ce, there is still no change because
nothing modifies REG_RCR or receive_config. For rtl8192cu, it now also
applies changes to rx_conf from configure_filter, but that can be
considered a bug which is fixed later.

Signed-off-by: Peter Wu <lekensteyn@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>