net: rfkill: Fix sparse warning in rfkill-regulator.c

'rfkill_regulator_ops' is used only in this file. Hence make it static.
Silences the following warning:
net/rfkill/rfkill-regulator.c:54:19: warning:
symbol 'rfkill_regulator_ops' was not declared. Should it be static?
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/rfkill/rfkill-regulator.c

@@ -51,7 +51,7 @@ static int rfkill_regulator_set_block(void *data, bool blocked)
 	return 0;
 }
 
-struct rfkill_ops rfkill_regulator_ops = {
+static struct rfkill_ops rfkill_regulator_ops = {
 	.set_block = rfkill_regulator_set_block,
 };