lossless_enc_sse2: harmonize function suffixes
lossless_enc_sse2: harmonize function suffixes

BUG=webp:355

Change-Id: I06c64416103c3f3fc0519dd46d64b0a35f9798e4

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