mfd: ac100: Convert to use maple tree register cache

The maple tree register cache is based on a much more modern data structure
than the rbtree cache and makes optimisation choices which are probably
more appropriate for modern systems than those made by the rbtree cache.

Signed-off-by: Bo Liu <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/ac100.c

···
 	.wr_table	= &ac100_writeable_table,
 	.volatile_table	= &ac100_volatile_table,
 	.max_register	= AC100_RTC_GP(15),
-	.cache_type	= REGCACHE_RBTREE,
+	.cache_type	= REGCACHE_MAPLE,
 };
 
 static struct mfd_cell ac100_cells[] = {