docs: tegra194-hte.rst: don't include gpiolib.c twice

docs: tegra194-hte.rst: don't include gpiolib.c twice

All extern functions of drivers/gpio/gpiolib.c are already
inside the Kernel documentation, as driver-api/gpio/index.rst
already includes it.

Placing a kernel-doc here will only cause mess, as the same symbol
will be placed on two parts of the document, causing breakages
in cross-references.

So, instead, add a cross-reference there.

This solves those Sphinx 3.1+ warnings:
    .../Documentation/driver-api/hte/tegra194-hte:28: ./drivers/gpio/gpiolib.c:2464: WARNING: Duplicate C declaration, also defined at driver-api/gpio/index:2464.
    .../Documentation/driver-api/hte/tegra194-hte:28: ./drivers/gpio/gpiolib.c:2493: WARNING: Duplicate C declaration, also defined at driver-api/gpio/index:2493.
    .../Documentation/driver-api/hte/tegra194-hte.rst:2464: WARNING: Duplicate C declaration, also defined at driver-api/gpio/index:2464.
    .../Documentation/driver-api/hte/tegra194-hte.rst:2464: WARNING: Duplicate C declaration, also defined at driver-api/gpio/index:2464.
    .../Documentation/driver-api/hte/tegra194-hte.rst:2464: WARNING: Duplicate C declaration, also defined at driver-api/gpio/index:2464.
    .../Documentation/driver-api/hte/tegra194-hte.rst:2493: WARNING: Duplicate C declaration, also defined at driver-api/gpio/index:2493.
    .../Documentation/driver-api/hte/tegra194-hte.rst:2493: WARNING: Duplicate C declaration, also defined at driver-api/gpio/index:2493.
    .../Documentation/driver-api/hte/tegra194-hte.rst:2493: WARNING: Duplicate C declaration, also defined at driver-api/gpio/index:2493.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: https://lore.kernel.org/r/de81b472f552bd651f140f0aa779a29652fffa62.1656759989.git.mchehab@kernel.org
Acked-by: Dipen Patel <dipenp@nvidia.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>