Cleanup uses of sprintf so we can deprecate it.

Also cleans up two instances of open() with useless mode params, and
changes a few uses of snprintf to use sizeof(buffer) instead of
hardcoded buffer sizes.

Change-Id: If11591003d910c995e72ad8f75afd072c255a3c5
diff --git a/toolbox/newfs_msdos.c b/toolbox/newfs_msdos.c
index 5b98a01..27ea9e8 100644
--- a/toolbox/newfs_msdos.c
+++ b/toolbox/newfs_msdos.c
@@ -695,7 +695,7 @@
                                                     (u_int)tm->tm_min));
                 mk4(bsx->volid, x);
                 mklabel(bsx->label, opt_L ? opt_L : "NO NAME");
-                sprintf(buf, "FAT%u", fat);
+                snprintf(buf, sizeof(buf), "FAT%u", fat);
                 setstr(bsx->type, buf, sizeof(bsx->type));
                 if (!opt_B) {
                     x1 += sizeof(struct bsx);