added stdio.h to includes for DBG compilation

src/drivers/bus/pci.c

@@ -19,6 +19,7 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include <stdio.h>
 #include <stdint.h>
 #include <string.h>
 #include <errno.h>

src/drivers/bus/pciextra.c

@@ -1,3 +1,4 @@
+#include <stdio.h>
 #include <stdint.h>
 #include <gpxe/pci.h>