net/wireless/reg.c: fix bad WARN_ON in if statement

fix:

  net/wireless/reg.c:348:29: error: macro "if" passed 2 arguments, but takes just 1

triggered by the branch-tracer.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: John W. Linville <linville@tuxdriver.com>