riscv: mm: Update the comment of CONFIG_PAGE_OFFSET

Since the commit 011f09d1 set sv57 as default for CONFIG_64BIT,
the comment of CONFIG_PAGE_OFFSET should be updated too.

Fixes: 011f09d1 ("riscv: mm: Set sv57 on defaultly")
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Link: https://lore.kernel.org/r/20230809031023.3575407-1-songshuaishuai@tinylab.org
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/page.h

@@ -33,8 +33,8 @@
 #define PAGE_OFFSET		_AC(CONFIG_PAGE_OFFSET, UL)
 #endif
 /*
- * By default, CONFIG_PAGE_OFFSET value corresponds to SV48 address space so
- * define the PAGE_OFFSET value for SV39.
+ * By default, CONFIG_PAGE_OFFSET value corresponds to SV57 address space so
+ * define the PAGE_OFFSET value for SV48 and SV39.
  */
 #define PAGE_OFFSET_L4		_AC(0xffffaf8000000000, UL)
 #define PAGE_OFFSET_L3		_AC(0xffffffd800000000, UL)