Address review comments

* zero key buffer on failure
* readability improvements
* psa_finish_key_creation adjustment after removing import_key_into_slot

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
diff --git a/tests/src/drivers/key_management.c b/tests/src/drivers/key_management.c
index 6ca03c6..9bef4b6 100644
--- a/tests/src/drivers/key_management.c
+++ b/tests/src/drivers/key_management.c
@@ -106,6 +106,10 @@
         {
             *key_length = bytes;
         }
+        else
+        {
+            memset( key, 0, bytes );
+        }
 
         mbedtls_ecp_keypair_free( &ecp );
         return( status );
@@ -146,7 +150,7 @@
         mbedtls_ecp_keypair ecp;
         psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
 
-        if( *bits == 0 )
+        if( psa_get_key_bits( attributes ) == 0 )
         {
             // Attempt auto-detect of curve bit size
             size_t curve_size = data_length;