cifs: smbd: Return -EINVAL when the number of iovs exceeds SMBDIRECT_MAX_SGE

commit 37941ea1

 upstream.

While it's not friendly to fail user processes that issue more iovs
than we support, at least we should return the correct error code so the
user process gets a chance to retry with smaller number of iovs.

Signed-off-by: Long Li <longli@microsoft.com>
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>