rtlwifi: Remove all remaining references to variable 'noise' in rtl_stats struct

This completes removal of all places that reference variable 'noise'
in the rtl_stats struct. The definition of the struct is unchanged.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>