powerpc/dart: Drop unnecessary call to kmemleak_no_scan()

Erhard reported that kmemleak was showing a warning at boot:

  kmemleak: Not scanning unknown object at 0xc00000007f000000
  CPU: 0 PID: 0 Comm: swapper Not tainted 5.19.0-rc3-PMacG5+ #2
  Call Trace:
   .dump_stack_lvl+0x7c/0xc4 (unreliable)
   .kmemleak_no_scan+0xe0/0x100
   .iommu_init_early_dart+0x2f0/0x924
   .pmac_probe+0x1b0/0x20c
   .setup_arch+0x1b8/0x674
   .start_kernel+0xdc/0xb74
   start_here_common+0x1c/0x44
  DART table allocated at: (____ptrval____)

Which he bisected to a change in kmemleak, commit
23c2d497

 ("mm: kmemleak: take a full lowmem check in kmemleak_*_phys()").

Because pmac_probe() is called before mem_topology_setup(), the min/
max PFN variables are still zero. That causes kmemleak_alloc_phys() to
ignore the allocation, because the checks against the PFN fail. Then
kmemleak_no_scan() can't find the allocation and prints warning.

Given that kmemleak_alloc_phys() is ignoring the allocation to begin
with, there's no need to call kmemleak_no_scan() at all, which avoids
the warning.

Reported-by: Erhard Furtner <erhard_f@mailbox.org>
Closes: https://lore.kernel.org/all/bug-216156-206035@https.bugzilla.kernel.org%2F/
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240419115913.3317575-1-mpe@ellerman.id.au