mfd: intel_soc_pmic_bxtwc: 64 bit bug in bxtwc_val_store()

The call to kstrtoul() will corrupt memory on 64 bit systems because an
int is 4 bytes and a long is 8.

Also it's not a good idea to let users trigger a dev_err() because it
just ends up flooding /var/log/messages so I removed the printk.

Fixes: 2ddd2086ea9c ('mfd: add Intel Broxton Whiskey Cove PMIC driver')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>