coresight: trbe: Add ISB after TRBLIMITR write

DEN0154 states that hardware will be allowed to ignore writes to TRB*
registers while the trace buffer is enabled. Add an ISB to ensure that
it's disabled before clearing the other registers.

This is purely defensive because it's expected that arm_trbe_disable()
would be called before teardown which has the required ISB.

Fixes: a2b579c4 ("coresight: trbe: Remove redundant disable call")
Signed-off-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250609-james-cs-trblimitr-isb-v1-1-3a2aa4ee6770@linaro.org