Fix fstab memory leak

When reading the fstab config file fails, fstab memory is not freed.
When fstab structure is no longer needed, only half of it is freed.

Free fstab memory in all cases (error or when it is no longer needed).

Change-Id: Ib0758a5aaa69505285bf64143632986a2dbbdccb
Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>