zd1211rw: do not ratelimit no-ops

It is rather confusing to see this in the log:
[  695.606877] __ratelimit: 40 callbacks suppressed
[  700.726878] __ratelimit: 40 callbacks suppressed

without ever seeing any actual message. This is because
zd1211rw doesn't compile out the net_ratelimit() call
properly if debugging is not enabled.

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