iommu/mediatek: Remove clk_disable in mtk_iommu_remove

In the Linux kernel, the following vulnerability has been resolved:

iommu/mediatek: Remove clk_disable in mtk_iommu_remove

After the commit b34ea31fe013 ("iommu/mediatek: Always enable the clk on
resume"), the iommu clock is controlled by the runtime callback.
thus remove the clk control in the mtk_iommu_remove.

Otherwise, it will warning like:

echo 14018000.iommu > /sys/bus/platform/drivers/mtk-iommu/unbind

[ 51.413044] ------------[ cut here ]------------
[ 51.413648] vpp0_smi_iommu already disabled
[ 51.414233] WARNING: CPU: 2 PID: 157 at */v5.15-rc1/kernel/mediatek/
drivers/clk/clk.c:952 clk_core_disable+0xb0/0xb8
[ 51.417174] Hardware name: MT8195V/C(ENG) (DT)
[ 51.418635] pc : clk_core_disable+0xb0/0xb8
[ 51.419177] lr : clk_core_disable+0xb0/0xb8
...
[ 51.429375] Call trace:
[ 51.429694] clk_core_disable+0xb0/0xb8
[ 51.430193] clk_core_disable_lock+0x24/0x40
[ 51.430745] clk_disable+0x20/0x30
[ 51.431189] mtk_iommu_remove+0x58/0x118
[ 51.431705] platform_remove+0x28/0x60
[ 51.432197] device_release_driver_internal+0x110/0x1f0
[ 51.432873] device_driver_detach+0x18/0x28
[ 51.433418] unbind_store+0xd4/0x108
[ 51.433886] drv_attr_store+0x24/0x38
[ 51.434363] sysfs_kf_write+0x40/0x58
[ 51.434843] kernfs_fop_write_iter+0x164/0x1e0