dma-buf: Restore the scatterlist entry count before freeing

dma_buf_phys_vec_to_sgt() clears orig_nents to mark the returned table
as DMA-only. Since sg_free_table() uses orig_nents to walk and free the
scatterlist, dma_buf_free_sgt() leaks the allocation on every successful
map/unmap cycle.

Restore orig_nents from nents before freeing the table. The helper
allocates the DMA list directly, so nents retains the allocation count,
including for chained scatterlists.


The reported kmemleak output was:

KMEMLEAK LEAK: 2 driver-related leak(s)
KMEMLEAK LEAK: unreferenced object 0xff11000125ceff00 (size 32):
KMEMLEAK LEAK:   comm dtr, pid 4432, jiffies 4295031027
KMEMLEAK LEAK:   hex dump (first 32 bytes):
KMEMLEAK LEAK:     02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
KMEMLEAK LEAK:     00 00 01 00 28 38 00 00 00 10 00 00 00 00 00 00  ....(8..........
KMEMLEAK LEAK:   backtrace (crc 4e8077f2):
KMEMLEAK LEAK:     __kmalloc_noprof+0x451/0x8b0
KMEMLEAK LEAK:     __sg_alloc_table+0x2a0/0x4d0
KMEMLEAK LEAK:     sg_alloc_table+0x24/0x170
KMEMLEAK LEAK:     dma_buf_phys_vec_to_sgt+0x84f/0xed0
KMEMLEAK LEAK:     0xffffffffa1ad21a8
KMEMLEAK LEAK:     dma_buf_map_attachment+0x138/0x690
KMEMLEAK LEAK:     ib_umem_dmabuf_map_pages+0x249/0xc90 [ib_core]
KMEMLEAK LEAK:     0xffffffffa138f8d2
KMEMLEAK LEAK:     0xffffffffa1396abe
KMEMLEAK LEAK:     0xffffffffa1331a5f
KMEMLEAK LEAK:     0xffffffffa13320dd
KMEMLEAK LEAK:     0xffffffffa1ad696d
KMEMLEAK LEAK:     0xffffffffa1acecc7
KMEMLEAK LEAK:     0xffffffffa1acfd17
KMEMLEAK LEAK:     __x64_sys_ioctl+0x72c/0x11f0
KMEMLEAK LEAK:     do_syscall_64+0xa1/0x4f0
KMEMLEAK LEAK: unreferenced object 0xff1100016dbf3a80 (size 32):
KMEMLEAK LEAK:   comm dtr, pid 4432, jiffies 4295034705
KMEMLEAK LEAK:   hex dump (first 32 bytes):
KMEMLEAK LEAK:     02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
KMEMLEAK LEAK:     00 20 10 00 28 38 00 00 00 10 00 00 00 00 00 00  . ..(8..........

Fixes: 3aa31a8bb11e ("dma-buf: provide phys_vec to scatter-gather mapping routine")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>