The commit 59afdc7b ("crypto:
api - Move module sig ifdef into accessor function") broke the
build when modules are completely disabled because we directly
dereference module->name.

This patch fixes this by using the accessor function module_name.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>