icecc-env: don't raise error when icecc not installed
When icecc is not installed, the `which icecc` command in icecc-env.sh
returns nonzero. This happens when environment is being sourced. When
the terminal has `set -e`, the whole script fails and terminal is
closed.
Fix this by ignoring errors from the which command.
Signed-off-by: Adam Trhon <adam.trhon@tbs-biometrics.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
