spi: spi-sun6i: sun6i_spi_fill_fifo(): remove not needed length argument

spi: spi-sun6i: sun6i_spi_fill_fifo(): remove not needed length argument

The function sun6i_spi_fill_fifo() is called with a length argument of
"sspi->fifo_depth" and "SUN6I_FIFO_DEPTH".

The driver reads the number of free bytes in the FIFO from the hardware and
uses the length argument to limit this value. This is not needed as the number
of free bytes in the FIFO is always less or equal the depth of the FIFO.

This patch removes the length argument and check.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20200706143443.9855-9-mkl@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>