staging: wilc1000: fix build failure

staging: wilc1000: fix build failure

allmodconfig build of alpha, m68k, m32r, tilepro has failed with the
error:
drivers/staging/wilc1000/wilc_wfi_cfgoperations.c: In function 'wilc_create_wiphy':
drivers/staging/wilc1000/wilc_wfi_cfgoperations.c:2632:13:
	error: 'struct wiphy' has no member named 'wowlan'

Looking at other drivers wowlan can be only used when CONFIG_PM is
defined.

Fixes: 73584a40d748 ("staging: wilc1000: add ops resuem/suspend/wakeup in cfg80211")
Cc: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>