cfg80211: Remove unnecessary ksize() call

This removes an unnecessary ksize() call. krealloc() will do this
test internally and won't perform any allocation if the space is
already sufficient to hold the data.
So remove the redundant check.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>