MIPS: Do not request resources for crashkernel if one isn't defined

When KEXEC is enabled but crashkernel details are not passed through the
kernel commandline unnecessary resources are requested (start==end==0)

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14607/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/setup.c

@@ -672,6 +672,9 @@ static void __init request_crashkernel(struct resource *res)
 {
 	int ret;
 
+	if (crashk_res.start == crashk_res.end)
+		return;
+
 	ret = request_resource(res, &crashk_res);
 	if (!ret)
 		pr_info("Reserving %ldMB of memory at %ldMB for crashkernel\n",