staging: vc04_services: remove odd vchiq_debugfs_top() wrapper

vchiq_debugfs_top() is only a wrapper around a pointer to a dentry, so
just use the dentry directly instead, making it a static variable
instead of part of a static structure.

This also removes the pointless BUG_ON() when checking that dentry as no
one should ever care if debugfs is working or not, and the kernel should
really not panic over something as trivial as that.

Suggested-by: Eric Anholt <eric@anholt.net>
Cc: Stefan Wahren <stefan.wahren@i2se.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Keerthi Reddy <keerthigd4990@gmail.com>
Cc: linux-rpi-kernel@lists.infradead.org
Cc: linux-arm-kernel@lists.infradead.org
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>