can: m_can: m_can_{read_fifo,echo_tx_event}(): shift timestamp to full 32 bits

In the Linux kernel, the following vulnerability has been resolved:

can: m_can: m_can_{read_fifo,echo_tx_event}(): shift timestamp to full 32 bits

In commit 1be37d3b0414 ("can: m_can: fix periph RX path: use
rx-offload to ensure skbs are sent from softirq context") the RX path
for peripheral devices was switched to RX-offload.

Received CAN frames are pushed to RX-offload together with a
timestamp. RX-offload is designed to handle overflows of the timestamp
correctly, if 32 bit timestamps are provided.

The timestamps of m_can core are only 16 bits wide. So this patch
shifts them to full 32 bit before passing them to RX-offload.