usb: cdns3: cdnsp-gadget: Provide function name for 'cdnsp_find_next_ext_cap()'

usb: cdns3: cdnsp-gadget: Provide function name for 'cdnsp_find_next_ext_cap()'

Fixes the following W=1 kernel build warning(s):

 drivers/usb/cdns3/cdnsp-gadget.c:59: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Cc: Pawel Laszczak <pawell@cadence.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Acked-by: Peter Chen <peter.chen@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210526130037.856068-24-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>