staging/lustre: Fix sparse error (signature mismatch)

lprocfs_wr_atomic is defined in
drivers/staging/lustre/lustre/obdclass/lprocfs_status.c with its second argument
with the __user attribute:

int lprocfs_wr_atomic(struct file *file, const char __user *buffer,
              unsigned long count, void *data)

but its declaration in drivers/staging/lustre/lustre/include/lprocfs_status.h does
not include the attribute. Make declaration and definition match.

Signed-off-by: L. Alberto Giménez <agimenez@sysvalve.es>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>