staging: greybus: loopback_test: fix device-name leak

All the device names were being always leaked. Also,
illegal free was being called upon namelist[n] which
was coincidentally NULL. The pointer to dirent structures
must be individually freed before freeing the pointer array.

Coccinelle Script:
@@
expression arr,ex1,ex2;
@@

for(ex1 = 0; ex1 < ex2; ex1++) { <...
  arr[
- ex2
+ ex1
  ]
  ...> }

Signed-off-by: Gargi Sharma <gs051095@gmail.com>
Reviewed by: Johan Hovold <johan@kernel.org>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>