hello_world: Use Makefile automatic variables

Fix a few whitespace issues while here.

Signed-off-by: Anton Blanchard <anton@linux.ibm.com>

hello_world/Makefile

@@ -2,8 +2,8 @@ ARCH = $(shell uname -m)
 ifneq ("$(ARCH)", "ppc64")
 ifneq ("$(ARCH)", "ppc64le")
 	CROSS_COMPILE ?= powerpc64le-linux-
-        endif
-        endif
+endif
+endif
 
 CC = $(CROSS_COMPILE)gcc
 LD = $(CROSS_COMPILE)ld
@@ -16,13 +16,13 @@ LDFLAGS = -T powerpc.lds
 all: hello_world.hex
 
 hello_world.elf: hello_world.o head.o console.o
-	$(LD) $(LDFLAGS) -o hello_world.elf hello_world.o head.o console.o
+	$(LD) $(LDFLAGS) -o $@ $^
 
 hello_world.bin: hello_world.elf
-	$(OBJCOPY) -O binary hello_world.elf hello_world.bin
+	$(OBJCOPY) -O binary $^ $@
 
 hello_world.hex: hello_world.bin
-	../scripts/bin2hex.py hello_world.bin > hello_world.hex
+	../scripts/bin2hex.py $^ > $@
 
 clean:
 	@rm -f *.o hello_world.elf hello_world.bin hello_world.hex