coresight: tmc: fix failure to disable/enable ETF after reading

ETF may fail to re-enable after reading, and driver->reading will
not be set to false, this will cause failure to enable/disable to ETF.
This change set driver->reading to false even if re-enabling fail.

Fixes: 669c4614 ("coresight: tmc: Don't enable TMC when it's not ready.")
Co-developed-by: Yuanfang Zhang <quic_yuanfang@quicinc.com>
Signed-off-by: Yuanfang Zhang <quic_yuanfang@quicinc.com>
Signed-off-by: Mao Jinlong <quic_jinlmao@quicinc.com>
[ Added a comment to explain why we ignore the error ]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250507063716.1945213-1-quic_jinlmao@quicinc.com