ext4: reduce stack usage in ext4_mpage_readpages()

ext4: reduce stack usage in ext4_mpage_readpages()

This function is very similar to do_mpage_readpage() and a similar
approach to that taken in commit 12ac5a65cb56 will work.  As in
do_mpage_readpage(), we only use this array for checking block contiguity
and we can do that more efficiently with a little arithmetic.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://patch.msgid.link/20240718223005.568869-1-willy@infradead.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>