Commit 
12cc54376768461533b55ada1b0b6d4979f40579 'omap3: overo: Select
fdtfile for expansion board' wrongly missed the operator in the fdtfile
test. Update the test to only overwrite an empty fdtfile environment
variable.
Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>
                        "run mmcboot;" \
                "fi;" \
                "if run loadzimage; then " \
-                       "if test $fdtfile; then " \
+                       "if test -z \"${fdtfile}\"; then " \
                                "setenv fdtfile omap3-${boardname}-${expansionname}.dtb;" \
                        "fi;" \
                        "if run loadfdt; then " \