pmdadm: Fix help text for sector count
pmdadm: Fix help text for sector count

Fix text in help related to dm.read_sector and dm.write_sector.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp