USB: SMSC_HSIC: Change gpio variable type from unsigned to int

of_get_named_gpio may return negative error code, hence, change
the type of variables used in the driver for gpios.

Change-Id: I1affc9591d36c6febe46ea14c9d31ac62d2eb620
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>