rtc: ds1685: remove set but unused variables

Fix the following warnings:
drivers/rtc/rtc-ds1685.c: In function ‘ds1685_rtc_read_time’:
drivers/rtc/rtc-ds1685.c:264:5: warning: variable ‘ctrlb’ set but not used [-Wunused-but-set-variable]
  264 |  u8 ctrlb, century;
      |     ^~~~~
drivers/rtc/rtc-ds1685.c: In function ‘ds1685_rtc_proc’:
drivers/rtc/rtc-ds1685.c:758:19: warning: variable ‘ctrlc’ set but not used [-Wunused-but-set-variable]
  758 |  u8 ctrla, ctrlb, ctrlc, ctrld, ctrl4a, ctrl4b, ssn[8];
      |                   ^~~~~
Cc: Joshua Kinard <kumba@gentoo.org>
Acked-By: Joshua Kinard <kumba@gentoo.org>
Link: https://lore.kernel.org/r/20191122102212.400158-4-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>