spi: spi-ti-qspi: Fix return value handling of wait_for_completion_timeout

spi: spi-ti-qspi: Fix return value handling of wait_for_completion_timeout

wait_for_completion_timeout() returns unsigned long not int.
It returns 0 if timed out, and positive if completed.
The check for <= 0 is ambiguous and should be == 0 here
indicating timeout which is the only error case.

Fixes: 5720ec0a6d26 ("spi: spi-ti-qspi: Add DMA support for QSPI mmap read")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Link: https://lore.kernel.org/r/20220411111034.24447-1-linmq006@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>