Revert "serial: imx: Update mctrl old_status on RTSD interrupt"

This reverts commit e1e87568 which is
commit 40d79033 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I37284d886dabab9e9b153c7aba3eaa8e14b3523f
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>