Fix Disk shader cache when accurate multiplication is off (#5711)

* renderer_opengl.cpp: fix sanitize_mul check for disk shader cache

* Partially revert "Band-aid solution for 'Disk Shader Cache' (#5188)"

This reverts commit 2e0ce86c9e.

* Disable `disk_shader_cache` checkbox when `hw_renderer` is off

src/citra_qt/configuration/configure_graphics.ui

@@ -121,7 +121,7 @@
        <item>
          <widget class="QCheckBox" name="toggle_disk_shader_cache">
            <property name="toolTip">
-             <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Reduce stuttering by storing and loading generated shaders to disk.&lt;/p&gt;&lt;p&gt;It cannot be used without Enable Hardware Shader or Accurate Multiplication.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
+             <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Reduce stuttering by storing and loading generated shaders to disk.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
            </property>
            <property name="text">
              <string>Use Disk Shader Cache</string>