USB: gadget: mbim: Avoid copying uninitialized data to userspace

A race condition bug in function 'mbim_bind_config' allows to
change 'mbim->xport' type to invalid value. This allows
mbim_ioctl() to copy the uninitialized data to userspace. Fix
this by avoiding copy_to_user() call when transport type is invalid.

Change-Id: If8e8b6d4e2c347e1aff529bed0a798128eaea07c
CRs-Fixed: 1102418
Signed-off-by: Arumuga Durai A <cadurai@codeaurora.org>