tinycrypt/hmac: Array compared to NULL has no effect

This commit fixes the issue reported by Coverity: an array compared
against NULL is always false.

Coverity-CID: 143687
Coverity-CID: 143737
Coverity-CID: 143740

Change-Id: Id94a144c47b3377876695e86da8c0c33a989ec99
Signed-off-by: Flavio Santes <flavio.santes@intel.com>
1 file changed