ppc64: use checksum_64.S from powerpc

as it is identical to checksum.S from ppc64.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index 30367a0..1f1f01b 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -2,12 +2,15 @@
 # Makefile for ppc-specific library files..
 #
 
+ifeq ($(CONFIG_PPC_MERGE),y)
 obj-y			:= strcase.o string.o
 obj-$(CONFIG_PPC32)	+= div64.o copy_32.o checksum_32.o
 obj-$(CONFIG_PPC64)	+= copypage_64.o copyuser_64.o memcpy_64.o \
-			   usercopy_64.o sstep.o checksum_64.o mem_64.o
+			   usercopy_64.o sstep.o mem_64.o
 obj-$(CONFIG_PPC_ISERIES) += e2a.o
 ifeq ($(CONFIG_PPC64),y)
 obj-$(CONFIG_SMP)	+= locks.o
 endif
+endif
 
+obj-$(CONFIG_PPC64)	+= checksum_64.o