target/file: fix inclusive vfs_fsync_range() end

Both of the file target's calls to vfs_fsync_range() got the end offset
off by one.  The range is inclusive, not exclusive.  It would sync a bit
more data than was required.

The sync path already tested the length of the range and fell back to
LLONG_MAX so I copied that pattern in the rw path.

This is untested. I found the errors by inspection while following other
code.

Signed-off-by: Zach Brown <zab@zabbo.net>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>