docs: filesystems: vfs: correct flag name

There is no flag REMAP_CAN_SHORTEN. Commit eca3654e3cc7 ("vfs: enable
remap callers that can handle short operations") that introduces this
text also introduces the flag REMAP_FILE_CAN_SHORTEN. Change the name
in the documentation accordingly.

Signed-off-by: Julia Lawall <[e-mail]>
Fixes: eca3654e3cc7 ("vfs: enable remap callers that can handle short operations")
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/filesystems/vfs.rst

···
 	before any bytes were remapped.  The remap_flags parameter
 	accepts REMAP_FILE_* flags.  If REMAP_FILE_DEDUP is set then the
 	implementation must only remap if the requested file ranges have
-	identical contents.  If REMAP_CAN_SHORTEN is set, the caller is
+	identical contents.  If REMAP_FILE_CAN_SHORTEN is set, the caller is
 	ok with the implementation shortening the request length to
 	satisfy alignment or EOF requirements (or any other reason).