checkasm: Improve --bench output

Before:

wiener_7tap_8bpc_c: 167336.7
wiener_7tap_8bpc_sse2: 26007.0
wiener_7tap_8bpc_ssse3: 18151.7
wiener_7tap_8bpc_avx2: 9977.3
wiener_7tap_8bpc_avx512icl: 4649.1

After:

wiener_7tap_8bpc_c:         167735.9 ( 1.00x)
wiener_7tap_8bpc_sse2:       25727.0 ( 6.52x)
wiener_7tap_8bpc_ssse3:      17897.2 ( 9.37x)
wiener_7tap_8bpc_avx2:        9268.5 (18.10x)
wiener_7tap_8bpc_avx512icl:   4504.6 (37.24x)