mfd: core: Un-constify mfd_cell.of_reg

Enable dynamically filling in the whole mfd_cell structure. All other
fields already allow that.

Fixes: 466a62d7 ("mfd: core: Make a best effort attempt to match devices with the correct of_nodes")
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Link: https://lore.kernel.org/r/b73fe4bc4bd6ba1af90940a640ed65fe254c0408.1693253717.git.mirq-linux@rere.qmqm.plSigned-off-by: Lee Jones <lee@kernel.org>

include/linux/mfd/core.h

@@ -92,7 +92,7 @@ struct mfd_cell {
 	 * (above) when matching OF nodes with devices that have identical
 	 * compatible strings
 	 */
-	const u64 of_reg;
+	u64 of_reg;
 
 	/* Set to 'true' to use 'of_reg' (above) - allows for of_reg=0 */
 	bool use_of_reg;