phy: phy-core-mipi-dphy.c: Correct reference version

The rest of the code refers to version 1.2 of the MIPI D-PHY
specification. But this comment refers to 2.1, while a sub comment of
the function refers to 1.2 again. Replace 2.1 with 1.2.

Signed-off-by: Sebastian Fricke <sebastian.fricke@posteo.net>
Link: https://lore.kernel.org/r/20210421041740.8451-1-sebastian.fricke@posteo.net


Signed-off-by: Vinod Koul <vkoul@kernel.org>