fs/sysv: Don't round down address for kunmap_flush_on_unmap()

The kernel virtual address passed to kunmap_flush_on_unmap() has no more
any need to be rounded down.

Therefore, delete the rounding down of "page_addr" when passed to
kunmap_local() in dir_put_page().

Don't backport without commit 88d7b120 ("highmem: round down the
address passed to kunmap_flush_on_unmap()").

Cc: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>