docs: infrastructure.rst: exclude device_link_state from device.h

This is already documented at device_link.rst, causing this
warning, due to a broken cross-reference:

	.../Documentation/driver-api/device_link.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/infrastructure'.
	Declaration is 'device_link_state'.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>