readahead: drop index argument of page_cache_async_readahead()

readahead: drop index argument of page_cache_async_readahead()

The index argument of page_cache_async_readahead() is just folio->index so
there's no point in passing is separately.  Drop it.

Link: https://lkml.kernel.org/r/20240625101909.12234-5-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Tested-by: Zhang Peng <zhangpengpeng0808@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>