riscv: mm: init: make pt_ops_set_[early|late|fixmap] static

These three functions are only used in init.c, so make them static.
Fix W=1 warnings like below:

arch/riscv/mm/init.c:721:13: warning: no previous prototype for function
'pt_ops_set_early' [-Wmissing-prototypes]
   void __init pt_ops_set_early(void)
               ^
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20220516143204.2603-1-jszhang@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/mm/init.c

@@ -879,7 +879,7 @@ static void __init create_fdt_early_page_table(pgd_t *pgdir, uintptr_t dtb_pa)
  * MMU is not enabled, the page tables are allocated directly using
  * early_pmd/pud/p4d and the address returned is the physical one.
  */
-void __init pt_ops_set_early(void)
+static void __init pt_ops_set_early(void)
 {
 	pt_ops.alloc_pte = alloc_pte_early;
 	pt_ops.get_pte_virt = get_pte_virt_early;
@@ -901,7 +901,7 @@ void __init pt_ops_set_early(void)
  * Note that this is called with MMU disabled, hence kernel_mapping_pa_to_va,
  * but it will be used as described above.
  */
-void __init pt_ops_set_fixmap(void)
+static void __init pt_ops_set_fixmap(void)
 {
 	pt_ops.alloc_pte = kernel_mapping_pa_to_va((uintptr_t)alloc_pte_fixmap);
 	pt_ops.get_pte_virt = kernel_mapping_pa_to_va((uintptr_t)get_pte_virt_fixmap);
@@ -919,7 +919,7 @@ void __init pt_ops_set_fixmap(void)
  * MMU is enabled and page table setup is complete, so from now, we can use
  * generic page allocation functions to setup page table.
  */
-void __init pt_ops_set_late(void)
+static void __init pt_ops_set_late(void)
 {
 	pt_ops.alloc_pte = alloc_pte_late;
 	pt_ops.get_pte_virt = get_pte_virt_late;