usbip: vudc: fix null pointer dereference on udc->lock

usbip: vudc: fix null pointer dereference on udc->lock

Currently the driver attempts to spin lock on udc->lock before a NULL
pointer check is performed on udc, hence there is a potential null
pointer dereference on udc->lock.  Fix this by moving the null check
on udc before the lock occurs.

Fixes: ea6873a45a22 ("usbip: vudc: Add SysFS infrastructure for VUDC")
Signed-off-by: Colin Ian King <[email protected]>
Acked-by: Shuah Khan <[email protected]>
Reviewed-by: Krzysztof Opasiak <[email protected]>
Cc: stable <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>