drivers/rtc/rtc-isl12022.c: use PTR_RET()

Use of PTR_RET() simplifies the code.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Roman Fietze <roman.fietze@telemotive.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>