hwmon: (ftsteutates) Fix potential memory access error

Using set_bit() to set a bit in an integer is not a good idea, since
the function expects an unsigned long as argument, which can be 64 bit
wide. Coverity reports this problem as

>>>     CID 1364488:  Memory - illegal accesses  (INCOMPATIBLE_CAST)
>>>     Pointer "&ret" points to an object whose effective type is "int"
>>>	(32 bits, signed) but is dereferenced as a wider "unsigned
+long" (64 bits, unsigned).  This may lead to memory corruption.
245                     set_bit(1, (unsigned long *)&ret);

Just use BIT instead.

Cc: Thilo Cestonaro <thilo@cestona.ro>
Fixes: 08426eda

 ("hwmon: Add driver for FTS BMC chip "Teutates"")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>