rtc: optee: fix error code in probe()

Return an error code if kthread_create() fails.  Currently the code
returns success.

Fixes: 6266aea8 ("rtc: optee: add alarm related rtc ops to optee rtc driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/21f1a18008f1bbc8f70d0bd5c05b72fbf5fc9c7d.1758182509.git.dan.carpenter@linaro.org


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>