hwc2: Fix compilation issue

Fixes the following error
external/libcxx/include/__tree:1817:22: error:
the specified comparator type does not provide a const call operator
[-Werror,-Wuser-defined-warnings]

Change-Id: Iac9c233c858c91d648b76bbb01ddc98388a1da73
CRs-Fixed: 2059251
1 file changed