Added a simple ls to a nonexistent directory for test 1.
In case the driver is broken for a nonexistent directory, U-boot
might crash.

Here is an example failed output:

=> # Test Case 1 - ls
=> ext4ls host 0:0
<DIR>       4096 .
<DIR>       4096 ..
<DIR>      16384 lost+found
<DIR>       4096 SUBDIR
      2621440000 2.5GB.file
         1048576 1MB.file
=> # In addition, test with a nonexistent directory to see if we crash.
=> ext4ls host 0:0 invalid_d
** Can not find directory. **
./test/fs/fs-test.sh: line 161: 25786 Segmentation fault      (core dumped) $UBOOT  <<EOF

Subsequent tests will fail if U-boot crashes.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Reviewed-by: Tom Rini <trini@konsulko.com>