According to the DT bindings, the "max-bitrate" property is optional.
However, when it is not present, a warning is printed.
Fix this by adding a missing check for -EINVAL.

Fixes: a4a86d27 ("phy: phy-can-transceiver: Add support for generic CAN transceiver driver")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/88e158f97dd52ebaa7126cd9631f34764b9c0795.1674037334.git.geert+renesas@glider.beSigned-off-by: Vinod Koul <vkoul@kernel.org>