vold: Check partitions 1-4 instead of 0-3

In mmc_bootstrap_mmcblk, bootstrap partitions 1-4 instead of 0-3, since
that's how the kernel labels them.  Additionally, use the NDOSPART constant
from diskmbr.h instead of hardcoding 4 when scanning partitions.
diff --git a/vold/mmc.c b/vold/mmc.c
index cbddb92..fcf7c2f 100644
--- a/vold/mmc.c
+++ b/vold/mmc.c
@@ -25,6 +25,7 @@
 #include "vold.h"
 #include "mmc.h"
 #include "media.h"
+#include "diskmbr.h" /* for NDOSPART */
 
 #define DEBUG_BOOTSTRAP 0
 
@@ -233,7 +234,7 @@
          *mmcblk_devname != '/'; mmcblk_devname--);
     mmcblk_devname++;
 
-    for (part_no = 0; part_no < 4; part_no++) {
+    for (part_no = 1; part_no <= NDOSPART; part_no++) {
         char part_file[255];
         sprintf(part_file, "/sys%s/%sp%d", devpath, mmcblk_devname, part_no);
         if (!access(part_file, F_OK)) {