docs: update pin-control.rst references

Changeset 5513b411 ("Documentation: rename pinctl to pin-control")
renamed: Documentation/driver-api/pinctl.rst
to: Documentation/driver-api/pin-control.rst.

Update the cross-references accordingly.

Fixes: 5513b411 ("Documentation: rename pinctl to pin-control")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/46ac2e918c7c4a4b701d54870f167b78466ec578.1621413933.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>