[dtc] Remove another bashism from run_tests.sh

[Jon Loeliger]

> Current we check for various error codes with [ $x == "NN" ].  However
> '==' is not actually a correct operator for the [ (test) command.  It
> should be either '=' for string comparison or '-eq' for integer
> comparison.  It appears that the bash builtin version of test
> implements '==' though, so we were getting away with it, as long as
> /bin/sh was bash - or the testsuite generated no errors.
> 
> This patch fixes the usage of test so that it should work on non-bash
> shells.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.  Sorry for the delay.

Thanks,
jdl