powerpc/powernv: don't create OPAL msglog sysfs entry if memcons init fails

When initialising OPAL interfaces, there is a possibility that
opal_msglog_init() may fail to initialise the msglog/memory console.

Fix opal_msglog_sysfs_init() so it doesn't try to create sysfs entry for
the msglog if this occurs.
Suggested-by: NJoel Stanley <joel@jms.id.au>
Fixes: 9b4fffa1 ("powerpc/powernv: new function to access OPAL msglog")
Signed-off-by: NAndrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/opal-msglog.c

@@ -128,6 +128,11 @@ void __init opal_msglog_init(void)
 
 void __init opal_msglog_sysfs_init(void)
 {
+	if (!opal_memcons) {
+		pr_warn("OPAL: message log initialisation failed, not creating sysfs entry\n");
+		return;
+	}
+
 	if (sysfs_create_bin_file(opal_kobj, &opal_msglog_attr) != 0)
 		pr_warn("OPAL: sysfs file creation failed\n");
 }