dfu: dfu_nand: reduce verbosity

In combination with multiple partitions in NAND, this printf() ends up
being more noise than helpful. Change it to debug() instead.

Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Acked-by: Lukasz Majewski <lukma@denx.de>
diff --git a/drivers/dfu/dfu_nand.c b/drivers/dfu/dfu_nand.c
index 0bfdbf9..b812a3d 100644
--- a/drivers/dfu/dfu_nand.c
+++ b/drivers/dfu/dfu_nand.c
@@ -214,7 +214,7 @@
 		part = simple_strtoul(s, &s, 10);
 
 		sprintf(mtd_id, "%s%d,%d", "nand", dev, part - 1);
-		printf("using id '%s'\n", mtd_id);
+		debug("using id '%s'\n", mtd_id);
 
 		mtdparts_init();