ARM: dts: keystone-k2l: fix mdio io start address

The K2L MDIO io space has different start address.
Hence, fix it to be 0x26200f00 according to TRM.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>