[PATCH] sh: update outdated reference to init_bootmem()

The bootmem allocator was replaced by memblock in commit
355c45affca7 ("mm: remove bootmem allocator implementation.")
and init_bootmem() no longer exists.  The comment in
early_reserve_mem() still describes a two-step bootmem
validation that no longer applies: the reservation is now a
single memblock_reserve() call.  Rewrite the comment to
describe what the reservation actually covers.

Assisted-by: unnamed:deepseek-v3.2 coccinelle
Signed-off-by: Kexin Sun <[email protected]>
---
 arch/sh/mm/init.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
index 464a3a63e2fa..c008db3d422e 100644
--- a/arch/sh/mm/init.c
+++ b/arch/sh/mm/init.c
@@ -242,10 +242,10 @@ static void __init early_reserve_mem(void)
 	start_pfn = PFN_UP(__pa(_end));
 
 	/*
-	 * Reserve the kernel text and Reserve the bootmem bitmap. We do
-	 * this in two steps (first step was init_bootmem()), because
-	 * this catches the (definitely buggy) case of us accidentally
-	 * initializing the bootmem allocator with an invalid RAM area.
+	 * Use memblock_reserve() to protect the kernel image (text
+	 * through bss).  The start address accounts for the zero-page
+	 * offset configured by the platform; the size is rounded up
+	 * past _end.
 	 */
 	memblock_reserve(start, (PFN_PHYS(start_pfn) + PAGE_SIZE - 1) - start);
 
-- 
2.25.1