hwmon/smsc47m1: Get rid of a useless mutex

hwmon/smsc47m1: Get rid of a useless mutex

The smsc47m1 driver uses a mutex to protect the accesses to the
hardware registers. It really doesn't need any protection, as the
register space is flat. Get rid of that mutex for a smaller and
faster driver.

Signed-off-by: Jean Delvare <khali@linux-fr.org>