mfd: Fix section mismatch warning in ab3550-core

This patch fixes:
WARNING: drivers/mfd/built-in.o(.data+0x9998): Section mismatch in reference from the variable ab3550_driver to the function .init.text:ab3550_probe()
The variable ab3550_driver references
the function __init ab3550_probe()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>