net: phy: Grammar update for comment in genphy_update_link

Enhance the grammar of the comment in genphy_update_link()
describing momentary link drop handling.

Found by inspection.

Signed-off-by: Simon Horman <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/phy/phy_device.c

···
 	/* The link state is latched low so that momentary link
 	 * drops can be detected. Do not double-read the status
 	 * in polling mode to detect such short link drops except
-	 * the link was already down.
+	 * if the link was already down.
 	 */
 	if (!phy_polling_mode(phydev) || !phydev->link) {
 		status = phy_read(phydev, MII_BMSR);