can: m_can: m_can_stop(): set device to software init mode before closing

There might be some requests pending in the buffer when the interface close
sequence occurs. In some devices, these pending requests might lead to the
module not shutting down properly when m_can_clk_stop() is called.

Therefore, move the device to init state before potentially powering it down.

Fixes: e0d1f481

 ("can: m_can: add Bosch M_CAN controller support")
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Acked-by: Dan Murphy <dmurphy@ti.com>
Link: https://lore.kernel.org/r/20200825055442.16994-1-faiz_abbas@ti.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>