of: make of_node_check_flag() device_node parameter const

The device_node argument isn't modified by of_node_check_flag(), so mark it
const.
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Link: https://lore.kernel.org/r/20211014173055.2117872-1-nathanl@linux.ibm.comSigned-off-by: Rob Herring <robh@kernel.org>

include/linux/of.h

@@ -185,7 +185,7 @@ static inline bool of_node_is_root(const struct device_node *node)
 	return node && (node->parent == NULL);
 }
 
-static inline int of_node_check_flag(struct device_node *n, unsigned long flag)
+static inline int of_node_check_flag(const struct device_node *n, unsigned long flag)
 {
 	return test_bit(flag, &n->_flags);
 }