qualcommax: ipq807x: fix mac setup for Linksys MX4200v2

qualcommax: ipq807x: fix mac setup for Linksys MX4200v2

Currently for Linksys MX4200v2 all u-boot ethXaddr variables share the same MAC address
and there is no need to check them one by one.

Signed-off-by: Paweł Owoc <frut3k7@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/16070
(cherry picked from commit 80c867815636cbf32e85b431c5d06c531e4a371e)
Signed-off-by: Rafal Boni <rafal.boni@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17889
Signed-off-by: Robert Marko <robimarko@gmail.com>