spl: mmc: Avoid size growth in spl_mmc_find_device() debug

The for() loop ends up being in the code even if the log_debug() does
nothing. Add a condition to fix this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/common/spl/spl_mmc.c b/common/spl/spl_mmc.c
index 1f69659..fe42301 100644
--- a/common/spl/spl_mmc.c
+++ b/common/spl/spl_mmc.c
@@ -81,8 +81,10 @@
 	struct uclass *uc;
 
 	log_debug("Selecting MMC dev %d; seqs:\n", mmc_dev);
-	uclass_id_foreach_dev(UCLASS_MMC, dev, uc)
-		log_debug("%d: %s\n", dev_seq(dev), dev->name);
+	if (_LOG_DEBUG) {
+		uclass_id_foreach_dev(UCLASS_MMC, dev, uc)
+			log_debug("%d: %s\n", dev_seq(dev), dev->name);
+	}
 	ret = mmc_init_device(mmc_dev);
 #else
 	ret = mmc_initialize(NULL);