iov_iter: remove setting of page->index

Nothing actually checks page->index, so just remove it.

Link: https://lkml.kernel.org/r/20241216161253.37687-1-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>