[Coverity CID :190949]Error handling issues in /tests/subsys/fs/nffs_fs_api/common/test_append.c

[mandarcthorat1]

Static code scan issues seen in File: /tests/subsys/fs/nffs_fs_api/common/test_append.c
Category: Error handling issues
Function: test_append
Component: Tests
CID: 190949
Please fix or provide comments to square it off in coverity in the link: https://scan9.coverity.com/reports.htm#v32951/p12996

[ceolin]

#13976