regulator: rpi-panel-attiny: 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://msgid.link/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/regulator/rpi-panel-attiny-regulator.c

···
 	.val_bits = 8,
 	.disable_locking = 1,
 	.max_register = REG_WRITE_DATA_L,
-	.cache_type = REGCACHE_RBTREE,
+	.cache_type = REGCACHE_MAPLE,
 };
 
 static int attiny_set_port_state(struct attiny_lcd *state, int reg, u8 val)