wandboard: Do not print error message when PMIC is absent

Only the wandboard revD1 boards have PMIC, so when running on a wandboard
of different revision the following error is always shown on every boot:

pmic_get() ret -19

Instead of printing this error message, move it to debug level instead.

Signed-off-by: Fabio Estevam <festevam@gmail.com>

board/wandboard/wandboard.c

@@ -363,7 +363,7 @@ int power_init_board(void)
 
 	ret = pmic_get("pfuze100@8", &dev);
 	if (ret < 0) {
-		printf("pmic_get() ret %d\n", ret);
+		debug("pmic_get() ret %d\n", ret);
 		return 0;
 	}