usbfs: simplify the lookup-by-minor routines

This patch (as1105) simplifies the lookup-by-minor-number code in
usbfs.  Instead of passing the minor number to the callback, which
must then reconstruct the entire dev_t value, the patch passes the
dev_t value directly.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>