powerpc/ptdump: Fix sparse warning in hashpagetable.c

As reported by sparse:

  arch/powerpc/mm/ptdump/hashpagetable.c:264:29: warning: restricted __be64 degrades to integer
  arch/powerpc/mm/ptdump/hashpagetable.c:265:49: warning: restricted __be64 degrades to integer
  arch/powerpc/mm/ptdump/hashpagetable.c:267:36: warning: incorrect type in assignment (different base types)
  arch/powerpc/mm/ptdump/hashpagetable.c:267:36:    expected unsigned long long [usertype]
  arch/powerpc/mm/ptdump/hashpagetable.c:267:36:    got restricted __be64 [usertype] v
  arch/powerpc/mm/ptdump/hashpagetable.c:268:36: warning: incorrect type in assignment (different base types)
  arch/powerpc/mm/ptdump/hashpagetable.c:268:36:    expected unsigned long long [usertype]
  arch/powerpc/mm/ptdump/hashpagetable.c:268:36:    got restricted __be64 [usertype] r

The values returned by plpar_pte_read_4() are CPU endian, not __be64, so
assigning them to struct hash_pte confuses sparse. As a minimal fix open
code a struct to hold the values with CPU endian types.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220202053039.691917-1-mpe@ellerman.id.au