update_kernel.sh: Remove trailing p in bootonce cgpt command

Passing --bootonce to update_kernel.sh fails with the following error:

    ERROR: cgpt add: Can't open /dev/mmcblk0p: No such file or directory

Removing the trailing p from FLAGS_device fixes the problem.

BUG=none
TEST=manual
Run update_kernel.sh with --bootonce and see that it completes
successfully.

Change-Id: I0cca4e1ad0d94ae40a4a392599bddc0bd6289b26
Signed-off-by: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/198432
Reviewed-by: Olof Johansson <olofj@chromium.org>
diff --git a/update_kernel.sh b/update_kernel.sh
index 764d6b5..c255388 100755
--- a/update_kernel.sh
+++ b/update_kernel.sh
@@ -122,7 +122,7 @@
 
 mark_boot_once() {
   local idx=${FLAGS_partition##*[^0-9]}
-  remote_sh cgpt add -i ${idx} -S 0 -T 1 -P 15 ${FLAGS_device}
+  remote_sh cgpt add -i ${idx} -S 0 -T 1 -P 15 ${FLAGS_device%p}
 }
 
 update_syslinux_kernel() {