Use minimum 20 bytes salt for RSA PSS.

This is for compatibility with Bouncy Castle.

Bug: 22492259
Change-Id: I753e5fd223404ba960b6a35862bbd20f519f369b
diff --git a/android_keymaster_test.cpp b/android_keymaster_test.cpp
index 3e9d125..9a76b1b 100644
--- a/android_keymaster_test.cpp
+++ b/android_keymaster_test.cpp
@@ -1373,7 +1373,7 @@
                     key_bits = digest_bits + 8 * (11 + 19);
                     break;
                 case KM_PAD_RSA_PSS:
-                    key_bits = digest_bits + 8 * 10;
+                    key_bits = digest_bits + 22 * 8;
                     break;
                 default:
                     FAIL() << "Missing padding";