sunrpc: potential memory leak in function rdma_read_xdr

In case the check on ch_count fails the cleanup path is skipped and the
previously allocated memory 'rpl_map', 'chl_map' is not freed.

Reported by Coverity.

Signed-off-by: Christian Engelmayer <christian.engelmayer@frequentis.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>