powerpc/powernv: Skip registering log region when CONFIG_PRINTK=n

When CONFIG_PRINTK=n, log_buf_addr_get() returns NULL and log_buf_len_get()
return 0. Check for these return values and skip registering the dump buffer.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Reviewed-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/opal.c

@@ -667,7 +667,13 @@ static void __init opal_dump_region_init(void)
 
 	/* Register kernel log buffer */
 	addr = log_buf_addr_get();
+	if (addr == NULL)
+		return;
+
 	size = log_buf_len_get();
+	if (size == 0)
+		return;
+
 	rc = opal_register_dump_region(OPAL_DUMP_REGION_LOG_BUF,
 				       __pa(addr), size);
 	/* Don't warn if this is just an older OPAL that doesn't