ion: correct the behaviour when allocating non-contig regions failed

Also need to clear bitmaps of secure_heap as we haven't used these chunks
when allocated size less than requested.
It is only for non-contig case.

Change-Id: I7a97ee430c66344e74e7db1994d72e8dd09a882f
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>