arch/risc-v/src/mpfs/mpfs_fpga_canfd.c: Improve interrupt and error h…

…andling

- Remove unnecessary looping in the interrupt handling
- Recover properly from the rx overflow error
- Check the RXMOF bit always to sychrnonize the RX frames to recover from any errors
- Clear the interrupts in a single place after the irq handler is finished

Signed-off-by: Jukka Laitinen <[email protected]>