lib: wrap crypt API to hide errno usage

In order to prevent using the global errno, replace it with a static
version and create a wrapper function which returns the error value.

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/test/lib/test_crypt.c b/test/lib/test_crypt.c
index 277e4ef..fb21edf 100644
--- a/test/lib/test_crypt.c
+++ b/test/lib/test_crypt.c
@@ -21,19 +21,39 @@
 static int lib_crypt(struct unit_test_state *uts)
 {
 	int equals = 0;
+	int err;
+
+	err = crypt_compare("", "password", &equals);
+	ut_assertf(err != 0, "crypt_compare successful but should not\n");
+	ut_assertf(equals != 1,
+		   "crypt_compare password hash matched but should not\n");
 
 	if (IS_ENABLED(CONFIG_CRYPT_PW_SHA256)) {
-		crypt_compare(
+		err = crypt_compare("$5$", "password", &equals);
+		ut_assertf(err == 0, "crypt-sha256 not successful\n");
+		ut_assertf(
+			equals != 1,
+			"crypt-sha256 password hash matched but should not\n");
+
+		err = crypt_compare(
 			"$5$rounds=640000$TM4lL4zXDG7F4aRX$JM7a9wmvodnA0WasjTztj6mxg.KVuk6doQ/eBhdcapB",
 			"password", &equals);
+		ut_assertf(err == 0, "crypt-sha256 failed: %d\n", err);
 		ut_assertf(equals == 1,
 			   "crypt-sha256 password hash didn't match\n");
 	}
 	equals = 0;
 	if (IS_ENABLED(CONFIG_CRYPT_PW_SHA512)) {
-		crypt_compare(
+		err = crypt_compare("$6$", "password", &equals);
+		ut_assertf(err == 0, "crypt-sha512 not successful\n");
+		ut_assertf(
+			equals != 1,
+			"crypt-sha512 password hash matched but should not\n");
+
+		err = crypt_compare(
 			"$6$rounds=640000$fCTP1F0N5JLq2eND$z5EzK5KZJA9JnOaj5d1Gg/2v6VqFOQJ3bVekWuCPauabutBt/8qzV1exJnytUyhbq3H0bSBXtodwNbtGEi/Tm/",
 			"password", &equals);
+		ut_assertf(err == 0, "crypt-sha512 failed: %d\n", err);
 		ut_assertf(equals == 1,
 			   "crypt-sha512 password hash didn't match\n");
 	}