qseecom: Check input buffer from IOCTL

IOCTL messages come with pointers to buffer, check these
buffer pointers prior to accessing it.

Change-Id: Ibd724a35682a6f8e4f6900c8404854a8b55c0c9a
Signed-off-by: Hariprasad Dhalinarasimha <hnamgund@codeaurora.org>