coresight: etm4x: improve clarity of etm4_os_unlock comment

coresight: etm4x: improve clarity of etm4_os_unlock comment

To improve clarity, let's update the comment for etm4_os_unlock
to use the name of the register as per the ETM architecture
specification.

The existing comment is also misleading as it suggests any value
written to TRCOSLAR unlocks the trace registers, however it must
be '0' - let's also correct this.

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20190829202842.580-13-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>