Input: iforce - clean up Makefile

Use <module>-y notation to specify list of objects comprising iforce
module and conditionally pull in USB and RS232 support.

Also remove custom compiler flags and rely on general makefile rules
for enabling warnings.
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/joystick/iforce/Makefile

@@ -4,17 +4,8 @@
 # By Johann Deneux <johann.deneux@gmail.com>
 #
 
-# Goal definition
-iforce-objs	:= iforce-ff.o iforce-main.o iforce-packets.o
-
 obj-$(CONFIG_JOYSTICK_IFORCE)	+= iforce.o
 
-ifeq ($(CONFIG_JOYSTICK_IFORCE_232),y)
-	iforce-objs += iforce-serio.o
-endif
-
-ifeq ($(CONFIG_JOYSTICK_IFORCE_USB),y)
-	iforce-objs += iforce-usb.o
-endif
-
-EXTRA_CFLAGS = -Werror-implicit-function-declaration
+iforce-y := iforce-ff.o iforce-main.o iforce-packets.o
+iforce-$(CONFIG_JOYSTICK_IFORCE_232)	+= iforce-serio.o
+iforce-$(CONFIG_JOYSTICK_IFORCE_USB)	+= iforce-usb.o