rtc-mrst: Fix section types

Fix the following section mismatch warning.

  WARNING: drivers/rtc/built-in.o(.data+0xa0): Section mismatch in reference from the variable vrtc_mrst_platform_driver to the function .init.text:vrtc_mrst_platform_probe()
  The variable vrtc_mrst_platform_driver references the function __init vrtc_mrst_platform_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: Major Lee <major_lee@wistron.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>