fuzzy_fastboot: fix off-by-one error in ParseArgs

The argument parser doesn't iterate over the last argument. Adjust the
loop condition to fix this.

Note: The last argument is usually --gtest_filter or some other gtest
flag. Those get evaluated by a different function, so that's why this
wasn't usually a problem. However, when one doesn't provide any gtest
flags (to run all the tests), or provides the arguments in a different
order, this becomes an issue.

Test: fuzzy_fastboot --serial=SERIAL runs all tests
Change-Id: Ic0767f63ccb6b10d931f7efd91ca2e40aed2899b