net: dsa: microchip: use DSA_TAG_PROTO without _VALUE define

Correct the use of define DSA_TAG_PROTO_LAN937X_VALUE to
DSA_TAG_PROTO_LAN937X to improve readability.

Signed-off-by: Sean Nyekjaer <sean@geanix.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Link: https://lore.kernel.org/r/20231206160124.1935451-1-sean@geanix.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>