rtc: m41t80: remove warnings and replace obsolete function

Replace the obsolete "simple_strtoul" function to "kstrtoul".
Remove some checkpatch's errors, warnings and checks :
   - alignment with open parenthesis
   - spaces around '<' and '<<'
   - blank line after structure
   - quoted string split across lines

Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>