This fixes a regression caused by 22c8ca78.

nobh_prepare_write() no longer marks the page uptodate, so
nobh_truncate_page() needs to do it.
Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>