autofs: update struct autofs_dev_ioctl in Documentation

autofs: update struct autofs_dev_ioctl in Documentation

Sync with changes made by commit 730c9eeca980 ("autofs4: improve
parameter usage") which introduced an union for various ioctl commands
instead of having statically named arg1,2.

This commit simply replaces arg1,2 with the corresponding fields without
changing semantics.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Tomohiro Kusumi <[email protected]>
Signed-off-by: Ian Kent <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>