UPSTREAM: coresight: tmc: Get rid of mode parameter for helper routines

Get rid of the superfluous mode parameter and the check for
the mode in tmc_etX_enable_sink_{perf/sysfs}. While at it, also
remove the unnecessary WARN_ON() checks.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit c38e505e27017268b86ca89e51582a57e67b39b7)

Change-Id: I0394e5dd6335d1764d2ee6526a1c32d62d661bcd