msm: vidc: Set "power_enabled" properly in venus HFI

In vidc driver, "power_enabled" is set to true, once regulators/clocks
are enabled and after some register writes. This causes
"__write_register" to fail even though clocks are enabled.
This change fixes the write/read register failure issue.

Change-Id: I04a4a3734500ca27e37e5371875649bbc87fef75
Signed-off-by: Sowmya Pandiri <spandiri@codeaurora.org>