powerpc mpc85xx: Fix infinite recursion in bus_adjust_resource method

The default case needs to call bus_generic_adjust_resource to pass the
request up the tree, not bus_adjust_resource which will just call this
method again.

Fixes: 5a7e717fb790 powerpc mpc85xx: Use bus_generic_rman_*
(cherry picked from commit 68a3ff041129208ea98a3bd5142061176ab4165e)