Fix Hippocampal SubField names to match output file names

Replaced underscores with dashes for certain FreeSurfer names for
hippocampal subfields that do not correctly match up with the actual
output mgz filenames.
"right_CA2_3" to "right_CA2-3"
"right_CA4_DG" to "right_CA4-DG"
"left_CA2_3" to "left_CA2-3"
"left_CA4_DG" to "left_CA4-DG"