fix pillar get function when using salt-ssh

Since there were some changes in ``salt.modules.pillar.get`` (i.e. added
``merge`` and ``delimiter`` arg) it seems that this module should also
be updated to use the new form of ``pillar.get`` function while
using salt via SSH (salt-ssh).
Merge pull request #18238 from slafs/salt-ssh-pillar-fix

fix pillar get function when using salt-ssh