kbuild: remove unnecessary variable initializaions

Clearing obj-y, obj-m, obj-n, obj- in each Makefile is
a useless habit.

They are non-exported variables; therefore they are always empty
whenever descending into each subdirectory.
(Moreorver, obj-y and obj-m are also set to empty at the beginning
of scripts/Makefile.build)

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Peter Foley <pefoley2@pefoley.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

arch/arm/plat-omap/Makefile

@@ -6,9 +6,6 @@ ccflags-$(CONFIG_ARCH_MULTIPLATFORM) := -I$(srctree)/arch/arm/plat-omap/include
 
 # Common support
 obj-y := sram.o dma.o counter_32k.o
-obj-m :=
-obj-n :=
-obj-  :=
 
 # omap_device support (OMAP2+ only at the moment)