dma buf scatter list is never freed, free it!

Orignally detected by kmemleak:
  backtrace:
    [<ffffff80088b7658>] kmemleak_alloc+0x50/0x84
    [<ffffff8008373284>] sg_kmalloc+0x38/0x60
    [<ffffff8008373144>] __sg_alloc_table+0x60/0x110
    [<ffffff800837321c>] sg_alloc_table+0x28/0x58
    [<ffffff800837336c>] __sg_alloc_table_from_pages+0xc0/0x1ac
    [<ffffff800837346c>] sg_alloc_table_from_pages+0x14/0x1c
    [<ffffff8008097a3c>] __iommu_get_sgtable+0x5c/0x8c
    [<ffffff800850a1d0>] fastrpc_dma_buf_attach+0x84/0xf8
    [<ffffff80085114bc>] dma_buf_attach+0x70/0xc8
    [<ffffff8008509efc>] fastrpc_map_create+0xf8/0x1e8
    [<ffffff80085086f4>] fastrpc_device_ioctl+0x508/0x900
    [<ffffff80082428c8>] compat_SyS_ioctl+0x128/0x200
    [<ffffff80080832c4>] el0_svc_naked+0x34/0x38
    [<ffffffffffffffff>] 0xffffffffffffffff
Reported-by: Mayank Chopra <mak.chopra@codeaurora.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20190829092926.12037-6-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>