[media] radio-sf16fmi: declare pnp_attached as static

drivers/media/radio/radio-sf16fmi.c:59:6: warning: symbol 'pnp_attached' was not declared. Should it be static?
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/radio/radio-sf16fmi.c

@@ -56,7 +56,7 @@ struct fmi
 
 static struct fmi fmi_card;
 static struct pnp_dev *dev;
-bool pnp_attached;
+static bool pnp_attached;
 
 #define RSF16_MINFREQ (87U * 16000)
 #define RSF16_MAXFREQ (108U * 16000)