[PATCH] mm: powerpc init_mm without ptlock

Restore an earlier mod which went missing in the powerpc reshuffle: the 4xx
mmu_mapin_ram does not need to take init_mm.page_table_lock.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>