powerpc/mem: Fix arch/powerpc/mm/mem.c:53:12: error: no previous prototype for 'creat...

powerpc/mem: Fix arch/powerpc/mm/mem.c:53:12: error: no previous prototype for 'create_section_mapping'

Commit 7f73d819039a ("powerpc/mem: Add back missing header to fix 'no
previous prototype' error") was supposed to fix the problem, but in
the meantime commit 9c9692ec570b ("mm: fix phys_to_target_node() and*
memory_add_physaddr_to_nid() exports") moved create_section_mapping()
prototype from asm/sparsemem.h to asm/mmzone.h

Fixes: 7f73d819039a ("powerpc/mem: Add back missing header to fix 'no previous prototype' error")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/025754fde3d027904ae9d0191f395890bec93369.1631541649.git.christophe.leroy@csgroup.eu