Fix ctad-maybe-unsupported warning

The upcoming compiler warns about the following code pattern:

frameworks/native/libs/gui/SurfaceComposerClient.cpp:192:5: error: 'lock_guard' may not intend to support class template argument deduction [-Werror,-Wctad-maybe-unsupported]                                                                                                                                                  std::lock_guard lock(mMutex);

Add explicit deduction guide to fix the warning.

Test: m checkbuild
Change-Id: I4b8b22cdd9b9714d0dfc56c1590a19fcdfbbeb07