staging: ti dspbridge: deh: ensure only tlb #0 is enabled

We don't want the DSP to continue writing into other mapped pages, no
matter how unlikely.

Based on extensive discussion with Fernando Guzman Lugo.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>