spi: a3700: Return correct value on timeout detection

When waiting for transfer completion, a3700_spi_wait_completion
returns a boolean indicating if a timeout occurred.

The function was returning 'true' everytime, failing to detect any
timeout.

This patch makes it return 'false' when a timeout is reached.

Signed-off-by: Maxime Chevallier <maxime.chevallier@smile.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org