mfd: lm3533: Expand control-bank accessors

Expand the control-bank accessors that were implemented using macros.
This allows the definitions of these exported functions to be found more
easily and specifically avoids a W=1 compiler warning due to the
redundant brightness sanity check:

drivers/mfd/lm3533-ctrlbank.c: In function 'lm3533_ctrlbank_set_brightness':
drivers/mfd/lm3533-ctrlbank.c:98:10: warning: comparison is always false due to limited range of data type [-Wtype-limits]
   98 |  if (val > LM3533_##_NAME##_MAX)     \
      |          ^
drivers/mfd/lm3533-ctrlbank.c:125:1: note: in expansion of macro 'lm3533_ctrlbank_set'
  125 | lm3533_ctrlbank_set(brightness, BRIGHTNESS);
      | ^~~~~~~~~~~~~~~~~~~

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>