The permissions being set during the creation of the inodes was updating
eventfs_inode attributes as well. Those attributes should only be touched
by the setattr or remount operations, not during the creation of inodes.
The eventfs_inode attributes should only be used to set the inodes and
should not be modified during the inode creation.

Simplify the code and fix the situation by:

 1) Removing the eventfs_find_events() and doing a simple lookup for
    the events descriptor in eventfs_get_inode()

 2) Remove update_events_attr() as the attributes should only be used
    to update the inode and should not be modified here.

 3) Add update_inode_attr() that uses the attributes to determine what
    the inode permissions should be.

 4) As the parent_inode of the eventfs_root_inode structure is no longer
    needed, remove it.

Now on creation, the inode gets the proper permissions without causing
side effects to the ei->attr field.

Link: https://lore.kernel.org/lkml/20240522165031.944088388@goodmis.org

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>