Btrfs: stop using vfs_read in send

Btrfs: stop using vfs_read in send

commit ed2590953bd06b892f0411fc94e19175d32f197a upstream.

Apparently we don't actually close the files until we return to userspace, so
stop using vfs_read in send.  This is actually better for us since we can avoid
all the extra logic of holding the file we're sending open and making sure to
clean it up.  This will fix people who have been hitting too many files open
errors when trying to send.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>