fs/bcachefs: Fix __wait_on_freeing_inode() definition of waitqueue entry

The following recent commit made DEFINE_WAIT_BIT() type requirements stricter:

  2382d68d ("sched: change wake_up_bit() and related function to expect unsigned long *")

.. which results in a build failure:

  > fs/bcachefs/fs.c: In function '__wait_on_freeing_inode':
  > fs/bcachefs/fs.c:281:31: error: initialization of 'long unsigned int *' from incompatible pointer type 'u32 *' {aka 'unsigned int *'} [-Wincompatible-pointer-types]
  >   281 |         DEFINE_WAIT_BIT(wait, &inode->v.i_state, __I_NEW);

Since this code relies on the waitqueue initialization within
inode_bit_waitqueue() anyway, the DEFINE_WAIT_BIT() initialization
is unnecessary - we can just declare a waitqueue entry.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Suggested-by: NeilBrown <neilb@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>