disp: msm: assign aspace to gem object for mmap buffer

During gem fault, aspace value is found to be NULL leading to
crash while requesting for pages. This change assigns aspace
to gem object before mapping the pages.

Change-Id: Ie99ddfef59ee4427aec053c84ef078027d2fb4cd
Signed-off-by: Yashwanth <yvulapu@codeaurora.org>