hwmon: (max6650) Fix checkpatch issues

Fixed:
ERROR: do not use assignment in if condition
ERROR: open brace '{' following struct go on the same line
ERROR: spaces required around that '||' (ctx:VxV)
ERROR: switch and case should be at the same indent
WARNING: simple_strtoul is obsolete, use kstrtoul instead

Cc: Hans J. Koch <hjk@hansjkoch.de>
Acked-by: Hans J. Koch <hjk@hansjkoch.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>