staging: olpc_dcon: fix sparse symbol not declared warning

This patch gets rid of the following sparse warning:

drivers/staging/olpc_dcon/olpc_dcon.c:787:19: warning: symbol 'dcon_driver' was not declared. Should it be static?
Signed-off-by: NMurilo Opsfelder Araujo <mopsfelder@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/olpc_dcon/olpc_dcon.c

@@ -780,7 +780,7 @@ static const struct i2c_device_id dcon_idtable[] = {
 };
 MODULE_DEVICE_TABLE(i2c, dcon_idtable);
 
-struct i2c_driver dcon_driver = {
+static struct i2c_driver dcon_driver = {
 	.driver = {
 		.name	= "olpc_dcon",
 		.pm = &dcon_pm_ops,