Fixes a segfault due to use-after-free on x86 & ARM in the test suite.

Index: mhash-0.9.9.9/src/hmac_test.c
===================================================================
--- mhash-0.9.9.9/src/hmac_test.c
+++ mhash-0.9.9.9/src/hmac_test.c	2020-04-01 00:04:44.039815882 +0200
@@ -76,8 +76,6 @@
 
 	/* Test No 2 */	
 	
-	mutils_memset(tmp, 0, sizeof(tmp));
-	
 	passlen=sizeof(KEY2) - 1;
 	password = (mutils_word8 *) mutils_malloc(passlen+1);
 	mutils_memcpy(password, KEY2, passlen);