msm: camera: fix gpio0 set down by mistake when gc0339 power off

Camera sensor gc0339 has no reset pin, and the default value of
gpio pin is 0. When power off, gpio0 will be pulled down by
mistake. Add some nonzero check before the operation.

CRs-Fixed: 523223
Change-Id: Ifde6b15446731e610e4635f790e880f35073f3a6
Signed-off-by: Wang Wenbin <wenbinw@codeaurora.org>