This commit fixes a typo in compare-and-swap when retrieving the
memory region associated with a displacement. It was erroneously 8
bytes instead of the datatype size. This can cause an incorrect RMA
range error when the compare-and-swap is less than 4 bytes from the
end of the region.
Fixedopen-mpi/ompi#2080
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>