can: mcp25xxfd: rx-path: reduce number of SPI core requests to set UINC bit

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.de


Tested-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>