NFSv4.2: Fix READ_PLUS smatch warnings

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: d3b00a802c845 ("NFS: Replace the READ_PLUS decoding code")
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>