Initialize key bits to max size + 1 in psa_import_key

In psa_import_key, the key bits value was uninitialized before
calling the secure element driver import function. There is a
potential issue if the driver returns PSA_SUCCESS without setting
the key bits. This shouldn't happen, but shouldn't be discounted
either, so we initialize the key bits to an invalid issue.

Author: dgreen-arm

library/psa_crypto.c

@@ -1835,7 +1835,7 @@ psa_status_t psa_import_key( const psa_key_attributes_t *attributes,
     if( driver != NULL )
     {
         const psa_drv_se_t *drv = psa_get_se_driver_methods( driver );
-        size_t bits;
+        size_t bits = PSA_MAX_KEY_BITS + 1;
         if( drv->key_management == NULL ||
             drv->key_management->p_import == NULL )
         {