initrdscripts: exec switch_root(8) instead of chroot(1)

This should address for NOR-flash systems the same problem that was
fixed for MMC-based systems in commit b5cbe9bbba67 ("phosphor-mmc-init:
exec switch_root(8) rather than chroot(1)").

By virtue of switch_root(8) wiping out everything in the old root it
also avoids wasting a few megabytes of memory keeping that filesystem
around without any way of reaching it.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Change-Id: Ib87c7dcacca45aff3fb2c3fbc288dbb80160a427
diff --git a/meta-phosphor/recipes-phosphor/initrdscripts/files/obmc-init.sh b/meta-phosphor/recipes-phosphor/initrdscripts/files/obmc-init.sh
index 2a32d26..f778f92 100644
--- a/meta-phosphor/recipes-phosphor/initrdscripts/files/obmc-init.sh
+++ b/meta-phosphor/recipes-phosphor/initrdscripts/files/obmc-init.sh
@@ -439,6 +439,4 @@
 	mount --move $f root/$f
 done
 
-# switch_root /root $init
-exec chroot /root $init
-
+exec switch_root /root $init