LoongArch: Code improvements in function pcpu_populate_pte()

Do some code improvements in function pcpu_populate_pte():
1. Add memory allocation failure handling;
2. Replace pgd_populate() with p4d_populate(), it will be useful if
   there are four-level page tables.
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/kernel/numa.c

@@ -73,32 +73,34 @@ void __init pcpu_populate_pte(unsigned long addr)
 	pmd_t *pmd;
 
 	if (p4d_none(*p4d)) {
-		pud_t *new;
-
-		new = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
-		pgd_populate(&init_mm, pgd, new);
+		pud = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
+		if (!pud)
+			panic("%s: Failed to allocate memory\n", __func__);
+		p4d_populate(&init_mm, p4d, pud);
 #ifndef __PAGETABLE_PUD_FOLDED
-		pud_init(new);
+		pud_init(pud);
 #endif
 	}
 
 	pud = pud_offset(p4d, addr);
 	if (pud_none(*pud)) {
-		pmd_t *new;
-
-		new = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
-		pud_populate(&init_mm, pud, new);
+		pmd = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
+		if (!pmd)
+			panic("%s: Failed to allocate memory\n", __func__);
+		pud_populate(&init_mm, pud, pmd);
 #ifndef __PAGETABLE_PMD_FOLDED
-		pmd_init(new);
+		pmd_init(pmd);
 #endif
 	}
 
 	pmd = pmd_offset(pud, addr);
 	if (!pmd_present(*pmd)) {
-		pte_t *new;
+		pte_t *pte;
 
-		new = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
-		pmd_populate_kernel(&init_mm, pmd, new);
+		pte = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
+		if (!pte)
+			panic("%s: Failed to allocate memory\n", __func__);
+		pmd_populate_kernel(&init_mm, pmd, pte);
 	}
 }