Fix "fs: convert core functions to zero_user_page"

The bug was introduced by 01f2705daf5a36208e69d7cf95db9c330f843af6.
It misses to convert the first argument, it should be "new_page".

This became a cause of fatfs corruption.

Cc: Nate Diller <nate.diller@gmail.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/buffer.c

@@ -2101,7 +2101,7 @@ int cont_prepare_write(struct page *page, unsigned offset,
 						PAGE_CACHE_SIZE, get_block);
 		if (status)
 			goto out_unmap;
-		zero_user_page(page, zerofrom, PAGE_CACHE_SIZE - zerofrom,
+		zero_user_page(new_page, zerofrom, PAGE_CACHE_SIZE - zerofrom,
 				KM_USER0);
 		generic_commit_write(NULL, new_page, zerofrom, PAGE_CACHE_SIZE);
 		unlock_page(new_page);