spi: spidev: remove unused completion

This removes an unused completion from spidev_sync.

It was introduced in

	commit 25d5cb4b ("spi: remove some spidev oops-on-rmmod paths")

and it was no longer used after:

	commit 98d6f479 ("spi: spidev: use spi_sync instead of spi_async")

Signed-off-by: Seraphime Kirkovski (Haapie) <kirkseraph@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>