rtc: isl12057: use PTR_ERR_OR_ZERO to fix coccinelle warnings

drivers/rtc/rtc-isl12057.c:278:1-3: WARNING: PTR_RET can be used

 Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: coccinelle/api/ptr_ret.cocci

CC: Arnaud Ebalard <arno@natisbad.org>
CC: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>