Fix "fs: convert core functions to zero_user_page"

The bug was introduced by 01f2705d

.
It misses to convert the first argument, it should be "new_page".

This became a cause of fatfs corruption.

Cc: Nate Diller <nate.diller@gmail.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>