Linux: fix zfs_uio_dio_check_for_zero_page

The intent here is to replace the zero page pointer in the array of
pointers to pages in the struct.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Pavel Snajdr <snajpa@snajpa.net>
Closes #16812
Closes #16689
Closes #16642