mm: folio_zero_user: open code range computation in folio_zero_user()

mm: folio_zero_user: open code range computation in folio_zero_user()

riscv64-gcc-linux-gnu (v8.5) reports a compile time assert in:

   r[2] = DEFINE_RANGE(clamp_t(s64, fault_idx - radius, pg.start, pg.end),
 		       clamp_t(s64, fault_idx + radius, pg.start, pg.end));

where it decides that pg.start > pg.end in:
  clamp_t(s64, fault_idx + radius, pg.start, pg.end));

where pg comes from:
  const struct range pg = DEFINE_RANGE(0, folio_nr_pages(folio) - 1);

That does not seem like it could be true. Even for pg.start == pg.end,
we would need folio_test_large() to evaluate to false at compile time:

  static inline unsigned long folio_nr_pages(const struct folio *folio)
  {
	if (!folio_test_large(folio))
		return 1;
	return folio_large_nr_pages(folio);
  }

Workaround by open coding the range computation. Also, simplify the type
declarations for the relevant variables.

[ankur.a.arora@oracle.com: remove unneeded cast, per David]
Link: https://lkml.kernel.org/r/20260206223801.2617497-1-ankur.a.arora@oracle.com
Link: https://lkml.kernel.org/r/20260206223801.2617497-1-ankur.a.arora@oracle.com
Link: https://lkml.kernel.org/r/20260128185943.2397128-1-ankur.a.arora@oracle.com
Fixes: 93552c9a3350 ("mm: folio_zero_user: cache neighbouring pages")
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202601240453.QCjgGdJa-lkp@intel.com/
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzessutek Wilk <konrad.wilk@oracle.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Li Zhe <lizhe.67@bytedance.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>