[dsme] Fix include path in dsme-plugin package config file. JB#49564

Use of headers from other dsme development packages requires e.g.

  #include <dsme/state.h>

To avoid conflicts with includes with generic names, make it so that
the same is required for dsme-plugin headers, e.g.

  #include <dsme-plugin/modules.h>

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>

dsme-plugin.pc.in

@@ -5,4 +5,4 @@ Name: dsme-plugin-devel
 Description: Header files for building DSME plugins
 Version: @VERSION@
 Requires:
-Cflags: -I${includedir}/dsme-plugin
+Cflags: -I${includedir}