[frameworks][base][hwui] re-fix -Wimplicit-int-float-conversion

A new instance snuck in since I haven't completed the platform toolchain
upgrade yet. There was imprecision in this call; accept it by making the
implicit cast explicit.

Bug: 139945549
Test: mm
Change-Id: Id704d9741b480eba4cf3955e70119d935776faf6
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>