gluon-luci-theme: more consistent button spacing

package/gluon-luci-theme/sass/cascade.scss

@@ -438,6 +438,7 @@ img.cbi-image-button {
 input.cbi-button {
   @include button;
 
+  margin-left: 0.5em;
   background-repeat: no-repeat;
 }
 
@@ -565,11 +566,6 @@ textarea {
   margin-bottom: 0.5em;
 }
 
-form > div > input[type=submit],
-form > div > input[type=reset] {
-  margin-left: 0.5em;
-}
-
 table td,
 table th {
   color: #000000;