ceph: fix pr_fmt() redefinition

The vfs merge caused a latent bug to show up:

   In file included from fs/ceph/super.h:4:0,
                    from fs/ceph/ioctl.c:3:
   include/linux/ceph/ceph_debug.h:4:0: warning: "pr_fmt" redefined [enabled by default]
    #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
    ^
   In file included from include/linux/kernel.h:13:0,
                    from include/linux/uio.h:12,
                    from include/linux/socket.h:7,
                    from include/uapi/linux/in.h:22,
                    from include/linux/in.h:23,
                    from fs/ceph/ioctl.c:1:
   include/linux/printk.h:214:0: note: this is the location of the previous definition
    #define pr_fmt(fmt) fmt
    ^

where the reason is that <linux/ceph_debug.h> is included much too late
for the "pr_fmt()" define.

The include of <linux/ceph_debug.h> needs to be the first include in the
file, but fs/ceph/ioctl.c had for some reason missed that, and it wasn't
noticeable until some unrelated header file changes brought in an
indirect earlier include of <linux/kernel.h>.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>