test: eth: Don't crash if env_get returns NULL

env_get can return NULL if it fails to find the variable. Check its result
before using it.

Fixes: 6d9764c2a87 ("dm: test: Add a new test case against dm eth codes for NULL pointer access")
Fixes: df33fd28897 ("test: eth: Add test for ethernet addresses")
Signed-off-by: Sean Anderson <seanga2@gmail.com>
1 file changed