h264_cabac: synchronize decode_significance_*_x86 conditionals

The definition and the call site where under different #ifdefs.

libavcodec/h264_cabac.c

@@ -1656,7 +1656,7 @@ decode_cabac_residual_internal(H264Context *h, DCTELEM *block,
             index[coeff_count++] = last;\
         }
         const uint8_t *sig_off = significant_coeff_flag_offset_8x8[MB_FIELD];
-#if ARCH_X86 && HAVE_7REGS && HAVE_EBX_AVAILABLE && !defined(BROKEN_RELOCATIONS)
+#if ARCH_X86 && HAVE_6REGS && !defined(BROKEN_RELOCATIONS)
         coeff_count= decode_significance_8x8_x86(CC, significant_coeff_ctx_base, index,
                                                  last_coeff_ctx_base, sig_off);
     } else {