mmc: rk_sdmmc: fix SW-IOMMU memory leak

mmc: rk_sdmmc: fix SW-IOMMU memory leak

We could quickly reproduce this bug by decrease IO_TLB_DEFAULT_SIZE
and manually disable mmc DTO interrupt which can make driver fall into
post_tmo all the time.

So, some of these dump for swiotlb we can get here due to no enough
IO_TLB can be used to map page for kernel space:

DMA: Out of SW-IOMMU space for 128 bytes at device ff0f0000.rksdmmc
DMA: Out of SW-IOMMU space for 128 bytes at device ff0f0000.rksdmmc
...
DMA: Out of SW-IOMMU space for 128 bytes at device ff0f0000.rksdmmc
DMA: Out of SW-IOMMU space for 128 bytes at device ff0f0000.rksdmmc

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Reported-and-tested-by: Jianhong Chen <chenjh@rock-chips.com>
Cc: Yao Xiao <xy@rock-chips.com>