tools/power/acpi: fix compilation error

If we compile tools/acpi target in the top source directory, we'd get a
compilation error showing as bellow:

# make tools/acpi
DESCEND power/acpi
DESCEND tools/acpidbg
CC tools/acpidbg/acpidbg.o
Assembler messages:
Fatal error: can't create /home/lzy/kernel-upstream/power/acpi/\
tools/acpidbg/acpidbg.o: No such file or directory
../../Makefile.rules:26: recipe for target '/home/lzy/kernel-upstream/\
power/acpi/tools/acpidbg/acpidbg.o' failed
make[3]: *** [/home/lzy/kernel-upstream//power/acpi/tools/acpidbg/\
acpidbg.o] Error 1
Makefile:19: recipe for target 'acpidbg' failed
make[2]: *** [acpidbg] Error 2
Makefile:54: recipe for target 'acpi' failed
make[1]: *** [acpi] Error 2
Makefile:1607: recipe for target 'tools/acpi' failed
make: *** [tools/acpi] Error 2

Fixes: d5a4b1a540b8 ("tools/power/acpi: Remove direct kernel source include reference")
Signed-off-by: Zhengyuan Liu <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

tools/power/acpi/Makefile.config

···
 
 OUTPUT=$(srctree)/
 ifeq ("$(origin O)", "command line")
-	OUTPUT := $(O)/power/acpi/
+	OUTPUT := $(O)/tools/power/acpi/
 endif
 #$(info Determined 'OUTPUT' to be $(OUTPUT))