NFSv4.2: Fix READ_PLUS smatch warnings

Smatch reports:
  fs/nfs/nfs42xdr.c:1131 decode_read_plus() warn: missing error code? 'status'

Which Dan suggests to fix by doing a hardcoded "return 0" from the
"if (segments == 0)" check.

Additionally, smatch reports that the "status = -EIO" assignment is not
used. This patch addresses both these issues.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Closes: https://lore.kernel.org/r/202305222209.6l5VM2lL-lkp@intel.com/
Fixes: d3b00a8 ("NFS: Replace the READ_PLUS decoding code")
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

Author: amschuma-ntap

fs/nfs/nfs42xdr.c

@@ -1056,13 +1056,12 @@ static int decode_read_plus(struct xdr_stream *xdr, struct nfs_pgio_res *res)
 	res->eof = be32_to_cpup(p++);
 	segments = be32_to_cpup(p++);
 	if (segments == 0)
-		return status;
+		return 0;
 
 	segs = kmalloc_array(segments, sizeof(*segs), GFP_KERNEL);
 	if (!segs)
 		return -ENOMEM;
 
-	status = -EIO;
 	for (i = 0; i < segments; i++) {
 		status = decode_read_plus_segment(xdr, &segs[i]);
 		if (status < 0)