misc: vmw_vmci: fix kernel info-leak by initializing dbells in vmci_ctx_get_chkpt_doorbells()

A kernel-infoleak was reported by syzbot, which was caused because
dbells was left uninitialized.
Using kzalloc() instead of kmalloc() fixes this issue.

Reported-by:  <syzbot+a79e17c39564bedf0930@syzkaller.appspotmail.com>
Tested-by:  <syzbot+a79e17c39564bedf0930@syzkaller.appspotmail.com>
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Link: https://lore.kernel.org/r/20201122224534.333471-1-anant.thazhemadam@gmail.com


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