xen/arm: Fix dev_is_dt macro definition

This macro is not currently used, but still has an error in it:
a missing parenthesis. Fix this, so the macro is properly defined.

Fixes: 6c5d3075d9 ("xen/arm: Introduce a generic way to describe device")

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Michal Orzel <michal.orzel@arm.com>

xen/include/asm-arm/device.h

@@ -27,7 +27,7 @@ typedef struct device device_t;
 
 /* TODO: Correctly implement dev_is_pci when PCI is supported on ARM */
 #define dev_is_pci(dev) ((void)(dev), 0)
-#define dev_is_dt(dev)  ((dev->type == DEV_DT)
+#define dev_is_dt(dev)  ((dev)->type == DEV_DT)
 
 enum device_class
 {