pci: Allow debug message output in pci_auto.c

Remove the '#undef DEBUG' in pci_auto.c so that we can enable debug
message output via '-DDEBUG'.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/pci/pci_auto.c b/drivers/pci/pci_auto.c
index e8da977..43965d8 100644
--- a/drivers/pci/pci_auto.c
+++ b/drivers/pci/pci_auto.c
@@ -14,7 +14,6 @@
 #include <errno.h>
 #include <pci.h>
 
-#undef DEBUG
 #ifdef DEBUG
 #define DEBUGF(x...) printf(x)
 #else