CVE-2024-42249 spi: don't unoptimize message in spi_async()

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

spi: don’t unoptimize message in spi_async()

Calling spi_maybe_unoptimize_message() in spi_async() is wrong because
the message is likely to be in the queue and not transferred yet. This
can corrupt the message while it is being used by the controller driver.

spi_maybe_unoptimize_message() is already called in the correct place
in spi_finalize_current_message() to balance the call to
spi_maybe_optimize_message() in spi_async().