hwmon: epm_adc: fix compilation warning

New version of gcc gives an uninitialized warning for
the array of adc data. Fix it.

Change-Id: Ic56a8d11b30920248ca756175847bd26381c7caa
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>
(cherry picked from commit ce16bfde8b16f6f1c7003061eec8e9f2fbb98d7c)