fuse: use freezable wait in fuse_get_req()

Use freezable wait in fuse_get_req() so that it won't block
the system from entering suspend:

 Freezing user space processes failed after 20.009 seconds
 Call trace:
  __switch_to+0xcc/0x168
  schedule+0x57c/0x1138
  fuse_get_req+0xd0/0x2b0
  fuse_simple_request+0x120/0x620
  fuse_getxattr+0xe4/0x158
  fuse_xattr_get+0x2c/0x48
  __vfs_getxattr+0x160/0x1d8
  get_vfs_caps_from_disk+0x74/0x1a8
  __audit_inode+0x244/0x4d8
  user_path_at_empty+0x2e0/0x390
  __arm64_sys_faccessat+0xdc/0x260

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>