phy: cadence: Sierra: Add missing clk_disable_unprepare() in .remove callback

commit 44d30d62 ("phy: cadence: Add driver for Sierra PHY") enabled
the clock in probe and failed to disable in remove callback. Add missing
clk_disable_unprepare() in cdns_sierra_phy_remove().

Fixes: 44d30d62

 ("phy: cadence: Add driver for Sierra PHY")
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Link: https://lore.kernel.org/r/20210319124128.13308-11-kishon@ti.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>