reiserfs: Fix vmalloc call under reiserfs lock

Vmalloc is called to allocate journal->j_cnode_free_list but
we hold the reiserfs lock at this time, which raises a
{RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} lock inversion.

Just drop the reiserfs lock at this time, as it's not even
needed but kept for paranoid reasons.

This fixes:

[ INFO: inconsistent lock state ]
2.6.33-rc5 #1
---------------------------------
inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
kswapd0/313 [HC0[0]:SC0[0]:HE1:SE1] takes:
 (&REISERFS_SB(s)->lock){+.+.?.}, at: [<c11118c8>]
reiserfs_write_lock_once+0x28/0x50
{RECLAIM_FS-ON-W} state was registered at:
  [<c104ee32>] mark_held_locks+0x62/0x90
  [<c104eefa>] lockdep_trace_alloc+0x9a/0xc0
  [<c108f7b6>] kmem_cache_alloc+0x26/0xf0
  [<c108621c>] __get_vm_area_node+0x6c/0xf0
  [<c108690e>] __vmalloc_node+0x7e/0xa0
  [<c1086aab>] vmalloc+0x2b/0x30
  [<c110e1fb>] journal_init+0x6cb/0xa10
  [<c10f90a2>] reiserfs_fill_super+0x342/0xb80
  [<c1095665>] get_sb_bdev+0x145/0x180
  [<c1...