CVE-2023-53724

In the Linux kernel, the following vulnerability has been resolved:

mfd: pcf50633-adc: Fix potential memleak in pcf50633_adc_async_read()

`req` is allocated in pcf50633_adc_async_read(), but
adc_enqueue_request() could fail to insert the `req` into queue.
We need to check the return value and free it in the case of failure.