x86: hevc_mc: replace simple leas by adds

lea is detrimental for those simple cases. No impact overall to
the change though.

Before:
15017 decicycles in q, 1016152 runs, 32424 skips
15382 decicycles in q_bi, 1013673 runs, 34903 skips
3713 decicycles in e, 2074534 runs, 22618 skips
3901 decicycles in e_bi, 2065509 runs, 31643 skips
7852 decicycles in q_uni, 520165 runs, 4123 skips
2398 decicycles in e_uni, 1043339 runs, 5237 skips

After:
14898 decicycles in q, 1016295 runs, 32281 skips
15119 decicycles in q_bi, 1015392 runs, 33184 skips
3682 decicycles in e, 2073224 runs, 23928 skips
3720 decicycles in e_bi, 2065043 runs, 32109 skips
7643 decicycles in q_uni, 520280 runs, 4008 skips
2363 decicycles in e_uni, 1043780 runs, 4796 skips