msm: sde: avoid request dereference with cached sequence id

Reference id is used by retire handler to signal completion
status. Reference id is currently retrieved directly from
core layer request structure; however, this structure can
be freed during stop streaming by core layer. To avoid
dereferencing core request structure, cache sequence id
during core request creation, and use the cached value to
update retire sequence.

Change-Id: I73be2c43b7375832be4463002441a02b1a426b2e
Signed-off-by: Alan Kwong <akwong@codeaurora.org>