wl1271: remove deprecated usage of RX status noise

The noise element in the ieee80211_rx_status struct has been deprecated in
commit "mac80211: deprecate RX status noise".  Remove the usage of this
element from wl1271_rx.c to avoid warnings.

Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Reviewed-by: Teemu Paasikivi <ext-teemu.3.paasikivi@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>