rescaler_sse2.c: fix WEBP_RESCALER_FIX -> _RFIX typo
rescaler_sse2.c: fix WEBP_RESCALER_FIX -> _RFIX typo

quiets -Wundef

Change-Id: I8f1facf401b6f1ab393005c93086ac3e2ae354d5

PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp