staging: most: usb: remove overcautious parameter checking

The interface pointer passed to a core API function cannot be NULL. This
patch removes unnessecary the sanity check of the pointer.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/1588672829-28883-2-git-send-email-christian.gromm@microchip.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>