mkfs.ubifs: Fix runtime assertions when running without crypto

mkfs.ubifs: Fix runtime assertions when running without crypto

Running mkfs.ubifs which was build without crypto triggered the
following assertion:

mkfs.ubifs: ubifs-utils/mkfs.ubifs/fscrypt.h:166:
inherit_fscrypt_context: Assertion `0' failed.

A previous commit-cc4c5e295f54 ("mkfs.ubifs: Enable support for building
without crypto") added a check for an existing fscrypt context before calling
functions inherit_fscrypt_context() and free_fscrypt_context(),
however did not properly do this for each call to these functions.

Fixes: cc4c5e295f54 ("mkfs.ubifs: Enable support for building without crypto")
Signed-off-by: Henri Roosen <henri.roosen@ginzinger.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>