Method 1: recode the race variables
See this data set:
Suppose the orange part represents the original data. The culprits that inflated the percentage are cases 4 and 5.
To recode them, first count the total response per case by adding across the columns, resulting is the column Sum. For those who has just 1, they chose only one race and will retain that race. For those with 2 or more, we will recode them into multi-racial, as suggested in the answer of @PeterFlom.
The coding scheme would be something like:
if white = 1 and sum = 1 then newRace = 1;
if black = 1 and sum = 1 then newRace = 2;
if asian = 1 and sum = 1 then newRace = 3;
if others = 1 and sum = 1 then newRace = 4;
if sum > 1 then newRace = 5;
You can see the newRace and its labeling scheme in blue. The frequency of the variable newRace should give percentages adding up to 100%. This method requires you to have executive level data, if you only have company level aggregated data, then it not possible to work this out without some assumptions.
Method 2: use the variables as is
In descriptive statistics table, it's also acceptable to footnote the table saying "percentages do not add up to 100% due to multiple choices."