blackfin/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: Steven Miao <realmz6@gmail.com>

arch/blackfin/include/asm/uaccess.h

@@ -147,7 +147,7 @@ static inline int bad_user_access_length(void)
 		}						\
 	} else							\
 		_err = -EFAULT;					\
-	x = (typeof(*(ptr)))_val;				\
+	x = (__force typeof(*(ptr)))_val;			\
 	_err;							\
 })