media: uvcvideo: Fix memory leak in uvc_gpio_parse

In the Linux kernel, the following vulnerability has been resolved: media: uvcvideo: Fix memory leak in uvc_gpio_parse Previously the unit buffer was allocated before checking the IRQ for privacy GPIO. In case of error, the unit buffer was leaked. Allocate the unit buffer after the IRQ to avoid it. Addresses-Coverity-ID: 1474639 ("Resource leak")