pkwrite: add newlines when calling mbedtls_pem_write_buffer()

New defines, which are shared with the pkparse module, lack the
new line so we manually add it when invoking
mbedtls_pem_write_buffer().

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/pkwrite.c b/library/pkwrite.c
index bd592f4..1f0d399 100644
--- a/library/pkwrite.c
+++ b/library/pkwrite.c
@@ -683,7 +683,7 @@
         goto cleanup;
     }
 
-    if ((ret = mbedtls_pem_write_buffer(PEM_BEGIN_PUBLIC_KEY, PEM_END_PUBLIC_KEY,
+    if ((ret = mbedtls_pem_write_buffer(PEM_BEGIN_PUBLIC_KEY "\n", PEM_END_PUBLIC_KEY "\n",
                                         output_buf + PUB_DER_MAX_BYTES - ret,
                                         ret, buf, size, &olen)) != 0) {
         goto cleanup;
@@ -712,18 +712,18 @@
 
 #if defined(MBEDTLS_RSA_C)
     if (pk_get_type_ext(key) == MBEDTLS_PK_RSA) {
-        begin = PEM_BEGIN_PRIVATE_KEY_RSA;
-        end = PEM_END_PRIVATE_KEY_RSA;
+        begin = PEM_BEGIN_PRIVATE_KEY_RSA "\n";
+        end = PEM_END_PRIVATE_KEY_RSA "\n";
     } else
 #endif
 #if defined(MBEDTLS_PK_HAVE_ECC_KEYS)
     if (pk_get_type_ext(key) == MBEDTLS_PK_ECKEY) {
         if (mbedtls_pk_is_rfc8410(key)) {
-            begin = PEM_BEGIN_PRIVATE_KEY_PKCS8;
-            end = PEM_END_PRIVATE_KEY_PKCS8;
+            begin = PEM_BEGIN_PRIVATE_KEY_PKCS8 "\n";
+            end = PEM_END_PRIVATE_KEY_PKCS8 "\n";
         } else {
-            begin = PEM_BEGIN_PRIVATE_KEY_EC;
-            end = PEM_END_PRIVATE_KEY_EC;
+            begin = PEM_BEGIN_PRIVATE_KEY_EC "\n";
+            end = PEM_END_PRIVATE_KEY_EC "\n";
         }
     } else
 #endif /* MBEDTLS_PK_HAVE_ECC_KEYS */