mfd: arizona: Fix typo using hard-coded register

mfd: arizona: Fix typo using hard-coded register

A hardcoded register is accidentally used instead of the register
address passed into the function. Correct this and use the appropriate
variable. This would cause minor issues on wm5102, but all other
devices using this driver would have been unaffected.

Fixes: commit 96ba8f2dfe1a ("mfd: arizona: Refactor arizona_poll_reg")
Reported-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>