usb4bsd/ehci: Ouch, fix a bug in the Makefile.

It was taking a wrong file and this caused ehci to not properly initialize
when loaded as a module (like it is our default).

Note that this is my fault, not Markus Pfeiffer's. I had messed with the
Makefiles and it was a copy/paste error.

Reported-by: ftigeot, tuxillo

sys/bus/u4b/controller/ehci/Makefile

@@ -1,6 +1,6 @@
 .PATH:	${.CURDIR}/..
 
 KMOD=	ehci
-SRCS=	ehci.c ohci_pci.c bus_if.h usb_if.h
+SRCS=	ehci.c ehci_pci.c bus_if.h usb_if.h
 
 .include <bsd.kmod.mk>