net: phy: correct spelling error of media in documentation

The header file incorrectly referenced "median-independant interface"
instead of media. Correct this typo.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Fixes: 4069a572

 ("net: phy: Document core PHY structures")
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20220309062544.3073-1-colin.foster@in-advantage.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>