phy: rockchip-typec: remove unused dfp variable

In order to silent the 'W=1' compile warning:

drivers/phy/rockchip/phy-rockchip-typec.c: In function 'tcphy_get_mode':
drivers/phy/rockchip/phy-rockchip-typec.c:625:7: warning: variable 'dfp'
set but not used [-Wunused-but-set-variable]

Cc: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>