Fix bash errors when the versions had differing number of elements.

Without this, I think things were still working, but I was getting this type of output:

```
./check_kernel: line 49: {version2[4]}=0: command not found
./check_kernel: line 51: [: : integer expression expected
./check_kernel: line 55: [: : integer expression expected
./check_kernel: line 49: {version2[5]}=0: command not found
./check_kernel: line 51: [: : integer expression expected
./check_kernel: line 55: [: : integer expression expected
OK - Running kernel: 2.6.32-504.1.3; available kernels:  2.6.32-431.20.3 2.6.32-504 2.6.32-504.1.3.
```

The assignment of these missing values of `0` didn't seem to be working with the curly braces. Removing those makes the assignment work as expected with no warning.