usb: gadget: uvc: Fix ERR_PTR dereference in uvc_v4l2.c

In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: uvc: Fix ERR_PTR dereference in uvc_v4l2.c

Fix potential dereferencing of ERR_PTR() in find_format_by_pix()

and uvc_v4l2_enum_format().

Fix the following smatch errors:

drivers/usb/gadget/function/uvc_v4l2.c:124 find_format_by_pix()

error: 'fmtdesc' dereferencing possible ERR_PTR()

drivers/usb/gadget/function/uvc_v4l2.c:392 uvc_v4l2_enum_format()

error: 'fmtdesc' dereferencing possible ERR_PTR()

Also, fix similar issue in uvc_v4l2_try_format() for potential

dereferencing of ERR_PTR().