hwmon: (sht15) Select CONFIG_BITREVERSE

If CONFIG_BITREVERSE is not built-in, the sht15 driver fails to link:

drivers/built-in.o: In function `sht15_crc8':
drivers/hwmon/sht15.c:195: undefined reference to `byte_rev_table'

This adds a Kconfig 'select' statement, like all other users of
bitrev.h have it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 33836ee9 ("hwmon:change sht15_reverse()")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>