wireless: fix ERP rate flags

In the rate API patch I accidentally reverted the test for
ERP rates, this fixes it. All rates except 1, 2, 5.5 and 11
MBit are ERP rates, not those.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>