The IRQ handler of the TRBE driver could race against the update_buffer()
in consuming the  IRQ. So, if the update_buffer() gets to processing the
TRBE irq, the TRBSR will be cleared. Thus by the time IRQ handler is
triggered, there is nothing to do there. Handle these cases and do not
disable the TRBE unnecessarily. Since the TRBSR can be read without
stopping the TRBE, we can check that before disabling the TRBE.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20210923143919.2944311-2-suzuki.poulose@arm.comSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>