sysreset: Fix unsupported request return values

The description of the sysreset request method in <sysreset.h> says that
the return value should be -EPROTONOSUPPORT if the requested reset type
is not supported by this device.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/sysreset/sysreset_x86.c b/drivers/sysreset/sysreset_x86.c
index 4936fdb..dc772b5 100644
--- a/drivers/sysreset/sysreset_x86.c
+++ b/drivers/sysreset/sysreset_x86.c
@@ -87,7 +87,7 @@
 			return ret;
 		return -EINPROGRESS;
 	default:
-		return -ENOSYS;
+		return -EPROTONOSUPPORT;
 	}
 
 	outb(value, IO_PORT_RESET);