arm64/uaccess: fix sparse errors

virtio wants to read bitwise types from userspace using get_user.  At the
moment this triggers sparse errors, since the value is passed through an
integer.

Fix that up using __force.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/uaccess.h

@@ -147,7 +147,7 @@ do {									\
 	default:							\
 		BUILD_BUG();						\
 	}								\
-	(x) = (__typeof__(*(ptr)))__gu_val;				\
+	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
 } while (0)
 
 #define __get_user(x, ptr)						\