phy: mapphone-mdm6600: Add missing description for some structure fields

phy: mapphone-mdm6600: Add missing description for some structure fields

We get warning with W=1 build:
drivers/phy/motorola/phy-mapphone-mdm6600.c:185: warning: Function
parameter or member 'val' not described in 'phy_mdm6600_cmd'
drivers/phy/motorola/phy-mapphone-mdm6600.c:200: warning: Function
parameter or member 'work' not described in 'phy_mdm6600_status'

Fix that by adding description for 'val' and 'work'

Link: https://lore.kernel.org/r/20200708132809.265967-2-vkoul@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>