cifs: Fix FALLOC_FL_INSERT_RANGE by setting i_size after EOF moved

Fix the cifs filesystem implementations of FALLOC_FL_INSERT_RANGE, in
smb3_insert_range(), to set i_size after extending the file on the server
and before we do the copy to open the gap (as we don't clean up the EOF
marker if the copy fails).

Fixes: 7fe6fe95

 ("cifs: add FALLOC_FL_INSERT_RANGE support")
Cc: stable@vger.kernel.org
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Paulo Alcantara <pc@manguebit.com>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: linux-mm@kvack.org
Signed-off-by: Steve French <stfrench@microsoft.com>