rtc: ds3234 doesn't link when built-in

When ds3234 is built-in, the final links fails with the following vague error
message:

`.exit.text' referenced in section `.data' of drivers/built-in.o: defined in discarded section `.exit.text' of drivers/built-in.o

ds3234_remove() cannot be marked __exit, as it's accessed via __devexit_p().
In addition, mark ds3234_probe() __devinit while we're at it.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>