lib: rsa: Print detailed error info in rsa_engine_init() on engine resolution failure

Signed-off-by: Csókás Bence <csokas.bence@prolan.hu>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/lib/rsa/rsa-sign.c b/lib/rsa/rsa-sign.c
index 7ae163f..858ad92 100644
--- a/lib/rsa/rsa-sign.c
+++ b/lib/rsa/rsa-sign.c
@@ -317,7 +317,8 @@
 
 	e = ENGINE_by_id(engine_id);
 	if (!e) {
-		fprintf(stderr, "Engine isn't available\n");
+		fprintf(stderr, "Engine '%s' isn't available\n", engine_id);
+		ERR_print_errors_fp(stderr);
 		return -1;
 	}