mm: sync rss in speculative page fault path

The speculative page fault path does not sync the
rss in task_struct to mm_struct leading to large
variance in the RSS values observed by userspace
tools and also in the OOM task dump.

Change-Id: Id45f1b9b0a51a9afffbaf8e65f5ef747d409d0d7
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>