docs: networking: device_drivers: fix bad usage of UTF-8 chars

Probably because the original file was pre-processed by some
tool, both i40e.rst and iavf.rst files are using this character:

	- U+2013 ('–'): EN DASH

meaning an hyphen when calling a command line application, which
is obviously wrong. So, replace them by an hyphen, ensuring
that it will be properly displayed as literals when building
the documentation.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/95eb2a48d0ca3528780ce0dfce64359977fa8cb3.1620744606.git.mchehab+huawei@kernel.org


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