setup-mel-builddir: Remove bash-specific syntax.

Remove the bash-specific test to ensure that this will work if
the system default shell is dash which is the default on new
Ubuntu installs.

Signed-off-by: Drew Moseley <drew_moseley@mentor.com>
Merge pull request #353 from drewmoseley/fix-bashism

setup-mel-builddir: Remove bash-specific syntax.