hwmon: Add helper to tell if a char is invalid in a name

HWMON device names are not allowed to contain "-* \t\n". Add a helper
which will return true if passed an invalid character. It can be used
to massage a string into a hwmon compatible name by replacing invalid
characters with '_'.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>