can: grcan: grcan_probe(): fix broken system id check for errata workaround needs

The systemid property was checked for in the wrong place of the device
tree and compared to the wrong value.

Fixes: 6cec9b07

 ("can: grcan: Add device driver for GRCAN and GRHCAN cores")
Link: https://lore.kernel.org/all/20220429084656.29788-3-andreas@gaisler.com
Cc: stable@vger.kernel.org
Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>