soc: hab: fix uninitialized variable and relocate vchan refcnt

Init hab msg pointer to avoid accessing an uninitialized
pointer.

The format specifier "%p" can leak kernel addresses. Use
"%pK" instead.

Check the status of the pfn_table, because of wrong pagetable
coming from the corresponding hab client unexpectedly.

Change-Id: Ic8c6ba0243d27007d014165f2869a5775a96c09d
Signed-off-by: Yajun Li <yajunl@codeaurora.org>