tee: optee: interruptible RPC sleep

Prior to this patch RPC sleep was uninterruptible since msleep() is
uninterruptible. Change to use msleep_interruptible() instead.

Signed-off-by: Tiger Yu <tigeryu99@hotmail.com>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>