mfd: max77686: Fix 'line over 80 chars' warning

This is part of an effort to clean-up the MFD subsystem.

+WARNING: line over 80 characters
+                                      &max77686_rtc_regmap_config);

total: 0 errors, 1 warnings, 299 lines checked

Signed-off-by: Lee Jones <lee.jones@linaro.org>