dt-bindings: cros-ec: Fix a typo in description

A 's/pf/of/' on rpmsg-name description.

Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220512013921.164637-2-swboyd@chromium.org