Fix overflow in path building

An incorrect size was causing an unsigned value
to wrap, causing it to write past the end of
the buffer.

Bug: 28085658
Change-Id: Ie9625c729cca024d514ba2880ff97209d435a165

sdcard/sdcard.c

diff --git a/sdcard/sdcard.c b/sdcard/sdcard.c
index 06452aa..123fce6 100644
--- a/sdcard/sdcard.c
+++ b/sdcard/sdcard.c
@@ -337,7 +337,7 @@
 
     ssize_t pathlen = 0;
     if (node->parent && node->graft_path == NULL) {
-        pathlen = get_node_path_locked(node->parent, buf, bufsize - namelen - 2);
+        pathlen = get_node_path_locked(node->parent, buf, bufsize - namelen - 1);
         if (pathlen < 0) {
             return -1;
         }