rtc: pcf8523: Fix GCC 12 warning

When building with automatic stack variable initialization, GCC 12
complains about variables defined outside of switch case statements.
Move variables outside the switch, which silences warnings:

./drivers/rtc/rtc-pcf8523.c:284:20: error: statement will never be executed [-Werror=switch-unreachable]
  284 |                 u8 mode;
      |

./drivers/rtc/rtc-pcf8523.c:245:21: error: statement will never be executed [-Werror=switch-unreachable]
  245 |                 u32 value;
      |                     ^~~~~

Signed-off-by: Victor Erminpour <victor.erminpour@oracle.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1644453027-886-1-git-send-email-victor.erminpour@oracle.com