mac80211: fix variable truncation on 32-bit

Stephen Rothwell reported these warnings from a 32-bit build:

  net/mac80211/mlme.c:1771: warning: left shift count >= width of type
  net/mac80211/mlme.c:1772: warning: left shift count >= width of type
  net/mac80211/mlme.c:1773: warning: left shift count >= width of type
  net/mac80211/mlme.c:1774: warning: left shift count >= width of type
  net/mac80211/mlme.c:1775: warning: left shift count >= width of type

This shows a bug in my code -- BIT(X) uses just "1 << X" which means
a 32-bit integer on 32-bit platforms, but the code here needs a u64
on all platforms. Fix this by using "1ULL << X" instead of BIT(X).

Thanks Stephen!

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>