ANDROID: scs: fix recursive spinlock in scs_check_usage

Use cmpxchg instead of a spinlock in scs_check_usage() to avoid
deadlocks.

Bug: 157781894
Change-Id: I1701ccaf25fdbd34ce4798c6f93e220b1565fb34
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Git-commit: e467b8c7
Git-repo: https://android.googlesource.com/kernel/common


[jshriram@codeaurora.org: cherry-pick]
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>