mfd: rc5t583: Set regmap config reg counts properly

Regmap config max_register field should contain number of
device last register, however num_reg_defaults_raw field
should be set to register count instead
(usually one register more than max_register).

rc5t583 driver had both of these fields set to the same value,
fix this by introducing separate defines for max register
number and total count of registers.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Lee Jones <lee.jones@linaro.org>