tests: Fix firmware-auto-efi-loader-path-nonstandard

This test is intended to simulate the use of an OVMF firmware
image installed under a non-standard path. In order to make
such a configuration work, the user would have to provide
additional information.

Right now it doesn't matter, because the configuration is
rejected anyway, but the behavior is going to change slightly
in the future. Prepare by making the configuration more
complete and realistic.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

tests/qemuxml2argvdata/firmware-auto-efi-loader-path-nonstandard.x86_64-latest.err

@@ -1 +1 @@
-loader attribute 'type' cannot be specified when firmware autoselection is enabled
+loader attribute 'readonly' cannot be specified when firmware autoselection is enabled

tests/qemuxml2argvdata/firmware-auto-efi-loader-path-nonstandard.xml

@@ -5,7 +5,7 @@
   <vcpu placement='static'>1</vcpu>
   <os firmware='efi'>
     <type arch='x86_64' machine='pc-q35-4.0'>hvm</type>
-    <loader>/path/to/OVMF_CODE.fd</loader>
+    <loader readonly='yes' type='pflash'>/path/to/OVMF_CODE.fd</loader>
   </os>
   <features>
     <acpi/>