NFSD/blocklayout: Fix minlength check in proc_layoutget

NFSD/blocklayout: Fix minlength check in proc_layoutget

The extent returned by the file system may have a smaller offset than
the segment offset requested by the client. In this case, the minimum
segment length must be checked against the requested range. Otherwise,
the client may not be able to continue the read/write operation.

Fixes: 8650b8a05850 ("nfsd: pNFS block layout driver")
Signed-off-by: Sergey Bashirov <sergeybashirov@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>