There doesn't seem to be a combination of clock settings that would produce 48MHz. Best I could get is 47.97 (which should be good enough for device although not for host). However when I set this up in PE window (I am using KDS studio PE project), when generating PE code I get an error message:
Generator failure. Unexpected status of script Doxygen\Common\DoxyGenComponentProg.prg. Please contact Freescale support.
Not sure if the error message has to do with the warning about the USB clock not being exactly 48 MHz though
On MK22F512 there are two extra choices fro MCG settings that are not on MK22F128. I wonder if there are some limitations with MK22F128FN with regard to USB that do not exist for MK22F512