mpc85xx: remove calibrate_decr
With upstream commit 0aafbdf35c75cbfec82636d01e6dc7950bc1507c , this is
now default. No need to override.
Signed-off-by: Rosen Penev <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/16345
Signed-off-by: Robert Marko <[email protected]>