can: tcan4x5x: tcan4x5x_bus: remove not needed read_flag_mask

With C99 initializers, all non mentioned members are initialzied to 0, so
remove not needed initialization of read_flag_mask.

Reviewed-by: Dan Murphy <dmurphy@ti.com>
Tested-by: Sean Nyekjaer <sean@geanix.com>
Link: https://lore.kernel.org/r/20201215231746.1132907-7-mkl@pengutronix.de


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>