iw: ps: fix "get power_save" documentation
iw: ps: fix "get power_save" documentation

This doesn't take any arguments, remove the "<param>"
string from the help.

Link: c6d3ebb9eb18c2cd4621c34a7972a3085c34d034@changeid
Signed-off-by: Johannes Berg <bff32994ff0f8d048f262a8388145a71b6071bfe@intel.com>

greearb/iw-ct,greearb/iw-ct