arm64: kexec: reduce calls to page_address()

In kexec_page_alloc(), page_address() is called twice.
This patch add a new variable to help to reduce calls
to page_address().

Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Link: https://lore.kernel.org/r/20211125170600.1608-3-rongwei.wang@linux.alibaba.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/machine_kexec.c

@@ -104,13 +104,15 @@ static void *kexec_page_alloc(void *arg)
 {
 	struct kimage *kimage = (struct kimage *)arg;
 	struct page *page = kimage_alloc_control_pages(kimage, 0);
+	void *vaddr = NULL;
 
 	if (!page)
 		return NULL;
 
-	memset(page_address(page), 0, PAGE_SIZE);
+	vaddr = page_address(page);
+	memset(vaddr, 0, PAGE_SIZE);
 
-	return page_address(page);
+	return vaddr;
 }
 
 int machine_kexec_post_load(struct kimage *kimage)