staging: lustre: Remove circular dependency on header

The following patch fixes a build error on sparc32. I think it should go to
stable 3.16.

Remove a circular dependency on atomic.h header file which leads to compilation
failure on sparc32 as reported here:
http://kisskb.ellerman.id.au/kisskb/buildresult/11340509/

The specific dependency is as follows:

In file included from arch/sparc/include/asm/smp_32.h:24:0,
                 from arch/sparc/include/asm/smp.h:6,
                 from arch/sparc/include/asm/switch_to_32.h:4,
                 from arch/sparc/include/asm/switch_to.h:6,
                 from arch/sparc/include/asm/ptrace.h:84,
                 from arch/sparc/include/asm/processor_32.h:16,
                 from arch/sparc/include/asm/processor.h:6,
                 from arch/sparc/include/asm/barrier_32.h:4,
                 from arch/sparc/include/asm/barrier.h:6,
                 from arch/sparc/include/asm/atomic_32.h:17,
                 from arch/sparc/include/asm/atomic.h:6,
                 from drivers/staging/lustre/lustre/obdclass/class_obd.c:38
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
CC: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/obdclass/class_obd.c

@@ -35,7 +35,7 @@
  */
 
 #define DEBUG_SUBSYSTEM S_CLASS
-# include <asm/atomic.h>
+# include <linux/atomic.h>
 
 #include "../include/obd_support.h"
 #include "../include/obd_class.h"