usbip: don't open-code sockfd_lookup/sockfd_put

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc drivers/staging/usbip/stub_dev.c
Simple merge

diff --cc drivers/staging/usbip/usbip_common.c
Simple merge

diff --cc drivers/staging/usbip/usbip_common.h
Simple merge

diff --cc drivers/staging/usbip/vhci_hcd.c
Simple merge

diff --cc drivers/staging/usbip/vhci_sysfs.c
Simple merge