source has moved.  reflect new locations in manual page.

Reference: /n/sources/patch/applied/usbmannit
Date: Sun Jun 24 15:58:10 CES 2012
Signed-off-by: quanstro@quanstro.net

--- /sys/man/3/usb	Sun Jun 24 15:57:47 2012
+++ /sys/man/3/usb	Sun Jun 24 15:57:46 2012
@@ -515,9 +515,9 @@
 .B #u/usb
 root of the USB interface
 .SH SOURCE
-.B /sys/src/9/pc/usb.h
+.B /sys/src/9/port/usb.h
 .br
-.B /sys/src/9/pc/devusb.c
+.B /sys/src/9/*/devusb.c
 .br
 .B /sys/src/9/pc/usb?hci.c
 .SH "SEE ALSO"