NFS: Fix /proc/PID/io read_bytes for buffered reads

Prior to commit 8786fde8 ("Convert NFS from readpages to
readahead"), nfs_readpages() used the old mm interface read_cache_pages()
which called task_io_account_read() for each NFS page read.  After
this commit, nfs_readpages() is converted to nfs_readahead(), which
now uses the new mm interface readahead_page().  The new interface
requires callers to call task_io_account_read() themselves.
In addition, to nfs_readahead() task_io_account_read() should also
be called from nfs_read_folio().

Fixes: 8786fde8 ("Convert NFS from readpages to readahead")
Link: https://lore.kernel.org/linux-nfs/CAPt2mGNEYUk5u8V4abe=5MM5msZqmvzCVrtCP4Qw1n=gCHCnww@mail.gmail.com/


Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>