hwmon: (menf21bmc) Include linux/err.h

Include linux/err.h to get the definitions for IS_ERR() PTR_ERR() and
ERR_PTR() used in the driver.

This fixes compilation on powerpc targets.
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@men.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/menf21bmc_hwmon.c

@@ -21,6 +21,7 @@
 #include <linux/jiffies.h>
 #include <linux/slab.h>
 #include <linux/i2c.h>
+#include <linux/err.h>
 
 #define DRV_NAME  "menf21bmc_hwmon"