networking: fix warning about unused label wake_up

Function ieee80211_reconfig in net/mac80211/util.c contains label wake_up
which is defined unconditionally, but only used with CONFIG_PM. Gcc
warns about this when CONFIG_PM is not defined.

This patch makes the label's definition dependent on CONFIG_PM too,
eliminating the warning.

The issue was apparently introduced in git commit
eecc4800.

Signed-off-by: Vincent Zweije <vincent@zweije.nl>
Signed-off-by: John W. Linville <linville@tuxdriver.com>