coresight: etm4x: Ensure valid drvdata and clock before clk_put()

This validates 'drvdata' and 'drvdata->pclk' clock before calling clk_put()
in etm4_remove_platform_dev(). The problem was detected using Smatch static
checker as reported.

Fixes: 73d779a0

 ("coresight: etm4x: Change etm4_platform_driver driver for MMIO devices")
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: James Clark <james.clark@arm.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lists.linaro.org/archives/list/coresight@lists.linaro.org/thread/G4N6P4OXELPLLQSNU3GU2MR4LOLRXRMJ/
Reviewed-by: James Clark <james.clark@arm.com>
Reviewed-by: Mike Leach <mike.leach@lnaro.org>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230817035926.157370-1-anshuman.khandual@arm.com