usb: phy: remove file names from heading comments

File names in the heading comments fell out of favor long ago, and these weren't
even changed when the drivers were moved from drivers/usb/otg/, so remove them
at last...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>