doc: fix spacing in parameter description

Fixes #6953

doc/doxygen/src/css/riot.css

@@ -488,6 +488,10 @@ dl.todo > dt {
 }
 .params .paramdir {
   font-family: Menlo, Monaco, Consolas, "Courier New", monospace;
+  padding-right: 0.5em;
+}
+.params .paramname {
+  padding-right: 2em;
 }
 .icon {
   font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;

doc/doxygen/src/css/riot.less

@@ -434,6 +434,10 @@ dl.todo > dt {
 }
 .params .paramdir {
   font-family: @font-family-monospace;
+  padding-right: 0.5em;
+}
+.params .paramname {
+  padding-right: 2em;
 }
 .icon {
   font-family: @font-family-base;