net/wireless/sysfs.c:108: warning: ‘wiphy_uevent’ defined but not used

when CONFIG_HOTPLUG=n is because the only usage site of this function
is #ifdef'ed as such, so let's #ifdef the definition also.
Signed-off-by: Satyam Sharma <satyam@infradead.org>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>