bt-power: set gpio 47 to default low level

The gpio 47 port is used for BT enable and control, and it's
default high level will cause 10ma leakage when system sleeps
and BT is off. Set gpio value to 0 in bt-power driver to fix
the leakage issue.

CRs-Fixed: 2321652

Change-Id: I6e8cf0930a7a488ac454390fdc8f1c3c67197caf
Signed-off-by: Liuliu Zhao <liulzhao@codeaurora.org>