fix: correctly use new get_csr syntax

Signed-off-by: Maximilian Deubel <maximilian.deubel@nordicsemi.no>

Author: maxd-nordic

src/nrfcloud_utils/device_credentials_installer.py

@@ -159,7 +159,7 @@ def get_csr(cred_if, custom_dev_id = "", sectag = 0, local = False):
         csr, local_priv_key = create_device_credentials.create_local_csr(cn = custom_dev_id)
     else:
         # Use AT commands to request a CSR.
-        csr_blob = cred_if.get_csr(sectag, custom_dev_id)
+        csr_blob = cred_if.get_csr(sectag, f"CN={custom_dev_id}")
 
         if csr_blob is None:
             logger.error('Failed to obtain CSR from device')