Fixup: Impl. MBEDTLS_PK_ECKEY, not MBEDTLS_PK_ECDSA, via TinyCrypt

The PK-type MBEDTLS_PK_ECDSA isn't really used by the library.
Especially, when parsing a generic EC key, a PK context of type
MBEDTLS_PK_ECKEY will be requested. Hence, to drop in TinyCrypt
for the legacy-ECC implementation, the PK type that TinyCrypt
implements must be MBEDTLS_PK_ECKEY.
diff --git a/library/pk.c b/library/pk.c
index da34e56..161a135 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -115,19 +115,21 @@
             return( &mbedtls_rsa_info );
 #endif
 #if defined(MBEDTLS_ECP_C)
-        case MBEDTLS_PK_ECKEY:
-            return( &mbedtls_eckey_info );
         case MBEDTLS_PK_ECKEY_DH:
             return( &mbedtls_eckeydh_info );
 #endif
-#if defined(MBEDTLS_USE_TINYCRYPT)
-        case MBEDTLS_PK_ECDSA:
-            return( &mbedtls_uecc_ecdsa_info );
-#else
 #if defined(MBEDTLS_ECDSA_C)
         case MBEDTLS_PK_ECDSA:
             return( &mbedtls_ecdsa_info );
 #endif
+#if defined(MBEDTLS_USE_TINYCRYPT)
+        case MBEDTLS_PK_ECKEY:
+            return( &mbedtls_uecc_eckey_info );
+#else /* MBEDTLS_USE_TINYCRYPT */
+#if defined(MBEDTLS_ECP_C)
+        case MBEDTLS_PK_ECKEY:
+            return( &mbedtls_eckey_info );
+#endif
 #endif /* MBEDTLS_USE_TINYCRYPT */
         /* MBEDTLS_PK_RSA_ALT omitted on purpose */
         default: