If the requested page is part of the previous multi-page folio, there
is no need to call read_mapping_folio() again.
Also, get rid of the remaining one of page->index [1] in our codebase.
[1] https://lore.kernel.org/r/Zp8fgUSIBGQ1TN0D@xxxxxxxxxxxxxxxxxxxx
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>