dw3000_stm: set sched_util_min attribute to 50

dw3000 worker thread has critical timing constraints needing core 0
to run hat higher clock on the bursty small task.

Set sched_util_min to 50 raising CPU freq to 930 MHz while those tasks
are scheduled.

Bug: 189899991
Signed-off-by: Thierry Strudel <tstrudel@google.com>
Change-Id: Ibdcf895de90fec8e5868065645f99f2a3f530463