misc: fastrpc: fix DMA address corruption due to find_vma misuse

In the Linux kernel, the following vulnerability has been resolved: misc: fastrpc: fix DMA address corruption due to find_vma misuse fastrpc_get_args() uses find_vma() to look up the VMA for a user-provided pointer and compute a DMA address offset. When the address falls in a gap before the returned VMA, (ptr & PAGE_MASK) - vma->vm_start underflows, corrupting the DMA address sent to the DSP. Replace find_vma() with vma_lookup(), which returns NULL when the address is not contained within any VMA.