pmic-voter: Add the votable name in debugfs

Add the votable name in the first line of the debug output. This helps
in understanding which voter the output is for.

Change-Id: I7c3d321f9f062037d85efba437a3fc1012b64d4b
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>