USB: HSIC: Fix setting of strobe and data gpios for HSIC host

Since the following commit I3e8828ddc232936df3e21c8e1158af92b16996a2
the ehci msm hsic host driver read device tree settings as the strobe
and the data gpios. In case that these gpios not exists in the device
tree the return value is negative. The return value was assigned to
unsigned variables, therefore the driver assumes that there are
such gpios.
This fix handles correctly the return value of the of_get_named_gpio.

Change-Id: Ia5dde57cc36438b977791df658375e0946123096
Signed-off-by: Ido Shayevitz <idos@codeaurora.org>