docs: networking: phy: add missing space

Missing space between "pins'" and "strength"

Signed-off-by: Casper Andersson <casper.casan@gmail.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20221004073242.304425-1-casper.casan@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>