coda: Convert coda_symlink_filler() to use folio_end_read()

coda: Convert coda_symlink_filler() to use folio_end_read()

This is slightly more efficient than separate calls to
folio_mark_uptodate() and folio_unlock(), and it's easier to read.
Get rid of the call to folio_set_error() as nobody will check this flag.

Cc: Jan Harkes <jaharkes@cs.cmu.edu>
Cc: coda@cs.cmu.edu
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20240530202110.2653630-3-willy@infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>