change compile example rules.

SConscript

@@ -3,7 +3,7 @@ from building import *
 cwd  = GetCurrentDir()
 
 src = Glob('src/bs8116a.c')
-if GetDepend(['PKG_USING_BS8116A']):
+if GetDepend(['PKG_USING_BS8116A_EXAMPLE']):
     src += Glob('samples/bs8116a_sample.c')
 
 CPPPATH = [cwd + '/inc']