[IA64] ia64/mm/init.c: fix section mismatches

This patch fixes the following section mismatches:

<--  snip  -->

...
WARNING: vmlinux.o(.text+0x5b5c2): Section mismatch: reference to .init.text:memmap_init_zone (between 'memmap_init' and 'virtual_memmap_init')
WARNING: vmlinux.o(.text+0x5b842): Section mismatch: reference to .init.text:memmap_init_zone (between 'virtual_memmap_init' and 'ia64_mmu_init')
...

<--  snip  -->

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>