pNFS: Add prepare commit trace to block/scsi layout

Replace dprintk with trace event in ext_tree_prepare_commit() function.

Co-developed-by: Konstantin Evtushenko <koevtushenko@yandex.com>
Signed-off-by: Konstantin Evtushenko <koevtushenko@yandex.com>
Signed-off-by: Sergey Bashirov <sergeybashirov@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250630183537.196479-4-sergeybashirov@gmail.com


Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>