extcon: max77693: Staticize default_init_data

Commit 0ec83bd246 ("extcon: max77693: Initialize register of MUIC
device to bring up it without platform data") added this structure
but forgot to make it static. Without this patch we get the following
warning:
drivers/extcon/extcon-max77693.c:41:26: warning:
symbol 'default_init_data' was not declared. Should it be static?

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>