staging/lustre/obdclass: fix build warning

While building with W=1 we were getting the warning:

drivers/staging/lustre/lustre/obdclass/cl_object.c:1056:16:
	warning: old-style function definition
 struct lu_env *cl_env_percpu_get()
                ^

Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Acked-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>