phy: qcom-ufs: Make ufs_qcom_phy_disable_iface_clk static

Fix sparse warning:

drivers/phy/qualcomm/phy-qcom-ufs.c:462:6:
 warning: symbol 'ufs_qcom_phy_disable_iface_clk' was not declared. Should it be static?

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>