arm64: dts: imx8mm-kontron: Fix CAN SPI clock frequency

The MCP2515 can be used with an SPI clock of up to 10 MHz. Set the
limit accordingly to prevent any performance issues caused by the
really low clock speed of 100 kHz.

This removes the arbitrarily low limit on the SPI frequency, that was
caused by a typo in the original dts.

Without this change, receiving CAN messages on the board beyond a
certain bitrate will cause overrun errors (see 'ip -det -stat link show
can0').

With this fix, receiving messages on the bus works without any overrun
errors for bitrates up to 1 MBit.

Fixes: 8668d8b2

 ("arm64: dts: Add the Kontron i.MX8M Mini SoMs and baseboards")
Cc: stable@vger.kernel.org
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>