arm64: simplify pgd_alloc

Currently pgd_alloc has a redundant NULL check in its return path that
can be removed with no ill effects. With that removed it's also possible
to return early and eliminate the new_pgd temporary variable.

This patch applies said modifications, making the logic of pgd_alloc
correspond 1-1 with that of pgd_free.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/pgd.c

@@ -32,17 +32,10 @@
 
 pgd_t *pgd_alloc(struct mm_struct *mm)
 {
-	pgd_t *new_pgd;
-
 	if (PGD_SIZE == PAGE_SIZE)
-		new_pgd = (pgd_t *)get_zeroed_page(GFP_KERNEL);
+		return (pgd_t *)get_zeroed_page(GFP_KERNEL);
 	else
-		new_pgd = kzalloc(PGD_SIZE, GFP_KERNEL);
-
-	if (!new_pgd)
-		return NULL;
-
-	return new_pgd;
+		return kzalloc(PGD_SIZE, GFP_KERNEL);
 }
 
 void pgd_free(struct mm_struct *mm, pgd_t *pgd)