qseecom: fix a common lib loading issue

cmnlib_ion_handle is only used within qseecom_load_commonlib_image()
and is not a shared resource, so change it to a local variable and
avoid potential reuse or free by another thread in case of reentrancy.

Change-Id: I9e1f25cd024a19a7379b7409bdc6521bcd8bcae5
Signed-off-by: Zhen Kong <zkong@codeaurora.org>