powerpc/lib: Do not include string.o in obj-y twice

In the Makefile, string.o (which is generated from string.S) is
included into the list of objects being built unconditionally
(obj-y) in line 12.

Additionally, if CONFIG_PPC64 is set, it is included again in
line 17.

This patch removes the latter unnecessary inclusion.
Signed-off-by: Andreas Ruprecht <rupran@einserver.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/lib/Makefile

@@ -14,8 +14,7 @@ obj-y			:= string.o alloc.o \
 obj-$(CONFIG_PPC32)	+= div64.o copy_32.o
 
 obj-$(CONFIG_PPC64)	+= copypage_64.o copyuser_64.o \
-			   usercopy_64.o mem_64.o string.o \
-			   hweight_64.o \
+			   usercopy_64.o mem_64.o hweight_64.o \
 			   copyuser_power7.o string_64.o copypage_power7.o
 ifeq ($(CONFIG_GENERIC_CSUM),)
 obj-y			+= checksum_$(CONFIG_WORD_SIZE).o