nfsd: don't ignore high bits of copy count

Note size_t is 32-bit on a 32-bit architecture, but cp_count is defined
by the protocol to be 64 bit, so we could be turning a large copy into a
0-length copy here.

Reported-by: <radchenkoy@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4proc.c

@@ -1383,7 +1383,7 @@ static void nfsd4_init_copy_res(struct nfsd4_copy *copy, bool sync)
 static ssize_t _nfsd_copy_file_range(struct nfsd4_copy *copy)
 {
 	ssize_t bytes_copied = 0;
-	size_t bytes_total = copy->cp_count;
+	u64 bytes_total = copy->cp_count;
 	u64 src_pos = copy->cp_src_pos;
 	u64 dst_pos = copy->cp_dst_pos;