iwlwifi: Fix built-in compilation of iwlcore

This patch fixes problem in Makefile that prevented
built-in compilation of iwlcore

Commit that caused this problem: eadd3c4b ("iwlwifi: make Makefile
more concise")
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Yi Zhu <yi.zhu@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wireless/iwlwifi/Makefile

-obj-$(CONFIG_IWLCORE)	:= iwlcore.o
+obj-$(CONFIG_IWLCORE)	+= iwlcore.o
 iwlcore-objs 		:= iwl-core.o iwl-eeprom.o iwl-hcmd.o
 iwlcore-$(CONFIG_IWLWIFI_DEBUGFS) += iwl-debugfs.o
 iwlcore-$(CONFIG_IWLWIFI_LEDS) += iwl-led.o