[ACPI] fix x86_64 mis-merge

arch/x86_64/kernel/Makefile

@@ -8,7 +8,7 @@ obj-y	:= process.o semaphore.o signal.o entry.o traps.o irq.o \
 		ptrace.o i8259.o ioport.o ldt.o setup.o time.o sys_x86_64.o \
 		x8664_ksyms.o i387.o syscall.o vsyscall.o \
 		setup64.o bootflag.o e820.o reboot.o warmreboot.o
-obj-y += mce.o acpi/
+obj-y += mce.o
 
 obj-$(CONFIG_MTRR)		+= ../../i386/kernel/cpu/mtrr/
 obj-$(CONFIG_ACPI_BOOT)		+= acpi/