debugfs: Fix the missing initializations in __debugfs_file_get()

both method table pointers in debugfs_fsdata need to be initialized,
obviously, and calculating the bitmap of present methods would also
go better if we start with initialized state.

Fixes: 41a0ecc0 ("debugfs: get rid of dynamically allocation proxy_ops")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/20250129191937.GR1977892@ZenIV


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>