USB: ehci-msm2: Fix GPIO usage

Code currently assumes that valid gpio number must always be non zero
which is not correct. Also change gpio_request to devm_gpio_request
to simplify error handling.

Change-Id: If4b4643d5a216f72a757b1d2ebca0d3a3f480466
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>