fanotify: fix copy_event_to_user() fid error clean up

Ensure that clean up is performed on the allocated file descriptor and
struct file object in the event that an error is encountered while copying
fid info objects. Currently, we return directly to the caller when an error
is experienced in the fid info copying helper, which isn't ideal given that
the listener process could be left with a dangling file descriptor in their
fdtable.

Fixes: 5e469c83 ("fanotify: copy event fid info to user")
Fixes: 44d705b0 ("fanotify: report name info for FAN_DIR_MODIFY event")
Link: https://lore.kernel.org/linux-fsdevel/YMKv1U7tNPK955ho@google.com/T/#m15361cd6399dad4396aad650de25dbf6b312288e
Link: https://lore.kernel.org/r/1ef8ae9100101eb1a91763c516c2e9a3a3b112bd.1623376346.git.repnop@google.com


Signed-off-by: Matthew Bobrowski <repnop@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>