powerpc/mm: fix redundant inclusion of pgtable-frag.o in Makefile

The patch identified below added pgtable-frag.o to obj-y
but some merge witchery kept it also for obj-CONFIG_PPC_BOOK3S_64

This patch clears the duplication.

Fixes: 737b434d ("powerpc/mm: convert Book3E 64 to pte_fragment")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/Makefile

@@ -12,7 +12,6 @@ obj-y				:= fault.o mem.o pgtable.o mmap.o \
 obj-$(CONFIG_PPC_MMU_NOHASH)	+= nohash/
 obj-$(CONFIG_PPC_BOOK3S_32)	+= book3s32/
 obj-$(CONFIG_PPC_BOOK3S_64)	+= book3s64/
-obj-$(CONFIG_PPC_BOOK3S_64)	+= pgtable-frag.o
 obj-$(CONFIG_NEED_MULTIPLE_NODES) += numa.o
 obj-$(CONFIG_PPC_MM_SLICES)	+= slice.o
 obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o