mfd: rk8xx: 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: Mark Brown <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/rk8xx-i2c.c

···
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = RK818_USB_CTRL_REG,
-	.cache_type = REGCACHE_RBTREE,
+	.cache_type = REGCACHE_MAPLE,
 	.volatile_reg = rk808_is_volatile_reg,
 };
 
···
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = RK805_OFF_SOURCE_REG,
-	.cache_type = REGCACHE_RBTREE,
+	.cache_type = REGCACHE_MAPLE,
 	.volatile_reg = rk808_is_volatile_reg,
 };
 
···
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = RK808_IO_POL_REG,
-	.cache_type = REGCACHE_RBTREE,
+	.cache_type = REGCACHE_MAPLE,
 	.volatile_reg = rk808_is_volatile_reg,
 };