coresight: tmc: Remove duplicate memset

The tmc_etr_enable_hw() fills the buffer with 0's before enabling
the hardware. So, we don't need an explicit memset() in
tmc_enable_etr_sink_sysfs() before calling the tmc_etr_enable_hw().
This patch removes the explicit memset from tmc_enable_etr_sink_sysfs.

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>