x86: hevc_deblock: remove unnecessary masking

The unpacks/shuffles later on makes it unnecessary.

Before:
1508 decicycles in h, 2096759 runs, 393 skips
2512 decicycles in v, 2095422 runs, 1730 skips

After:
1477 decicycles in h, 2096745 runs, 407 skips
2484 decicycles in v, 2095297 runs, 1855 skips

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>