mm: cma: fix deadlock on s_follow_page_lock

mm: cma: fix deadlock on s_follow_page_lock

unlock s_follow_page_lock before jump to next_page label,
else any subsequent mutex_lock() on this lock will be waiting
infinitely causing deadlock.

Bug 1550455
Bug 200043261

Change-Id: I62689f808a133d3b491fc4044040f9c7275302e8
Signed-off-by: Sri Krishna chowdary <schowdary@nvidia.com>
Reviewed-on: http://git-master/r/554720
Reviewed-by: Peter Newman <pnewman@nvidia.com>
Tested-by: Peter Newman <pnewman@nvidia.com>
Reviewed-by: Vandana Salve <vsalve@nvidia.com>
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>