swiotlb: fix out-of-bounds TLB allocations with CONFIG_SWIOTLB_DYNAMIC

In the Linux kernel, the following vulnerability has been resolved: swiotlb: fix out-of-bounds TLB allocations with CONFIG_SWIOTLB_DYNAMIC Limit the free list length to the size of the IO TLB. Transient pool can be smaller than IO_TLB_SEGSIZE, but the free list is initialized with the assumption that the total number of slots is a multiple of IO_TLB_SEGSIZE. As a result, swiotlb_area_find_slots() may allocate slots past the end of a transient IO TLB buffer.