can: mcp251x: Use readx_poll_timeout() helper

We may use special helper macro to poll IO till condition or timeout occurs.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200217161038.25009-1-andriy.shevchenko@linux.intel.com


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