staging: tidspbridge: protect dmm_map properly

We need to protect not only the dmm_map list, but the individual
map_obj's, otherwise, we might be building the scatter-gather list with
garbage. So, use the existing proc_lock for that.

I observed race conditions which caused kernel panics while running
stress tests, also, Tuomas Kulve found it happening quite often in
Gumstix Over. This patch fixes those.

Cc: Tuomas Kulve <tuomas@kulve.fi>
Signed-off-by: Felipe Contreras <felipe.contreras@nokia.com>
Signed-off-by: Omar Ramirez Luna <omar.ramirez@ti.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>