Reduce the number of separate SPI core requests when setting the UINC bit in
the RX FIFO, and instead batch them up into a single SPI core request.

Link: https://github.com/marckleinebudde/linux/issues/4
Link: https://lore.kernel.org/r/20201126132144.351154-3-mkl@pengutronix.deTested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Ursula Maplehurst <ursula@kangatronix.co.uk>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>