iio: iadc: wait_for_completion_timeout time in jiffies

The timeout value to wait_for_completion_timeout is in jiffies but
the value being passed seems like it was intended to by microseconds
Note that the timeout was extremely long thus it might be too short
now. In any case it probably should be passed through usecs_to_jiffies()
or msecs_to_jiffies()

patch is against linux-next 3.19.0-rc1 -next-20141226

patch was only compile-tested x86_64_defcofnig + CONFIG_SPMI=m
CONFIG_IIO=m, CONFIG_QCOM_SPMI_IADC=m

Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Acked-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>