staging: lustre: potential underflow in libcfs_kkuc_group_add()

My static checker says that "group" is a user controlled number that can
be negative leading to an array underflow.  I have looked at it, and I'm
not an expert enough in lustre to say for sure if it is really a bug.
Anyway, it's simple enough to make the variable unsigned which pleases
the static checker and makes it easier to audit.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/include/linux/libcfs/libcfs_kernelcomm.h

@@ -91,7 +91,7 @@ typedef int (*libcfs_kkuc_cb_t)(__u32 data, void *cb_arg);
 /* Kernel methods */
 int libcfs_kkuc_msg_put(struct file *fp, void *payload);
 int libcfs_kkuc_group_put(int group, void *payload);
-int libcfs_kkuc_group_add(struct file *fp, int uid, int group,
+int libcfs_kkuc_group_add(struct file *fp, int uid, unsigned int group,
 				 __u32 data);
 int libcfs_kkuc_group_rem(int uid, int group);
 int libcfs_kkuc_group_foreach(int group, libcfs_kkuc_cb_t cb_func,

drivers/staging/lustre/lustre/libcfs/kernel_user_comm.c

@@ -110,7 +110,8 @@ static DECLARE_RWSEM(kg_sem);
  * @param uid identifier for this receiver
  * @param group group number
  */
-int libcfs_kkuc_group_add(struct file *filp, int uid, int group, __u32 data)
+int libcfs_kkuc_group_add(struct file *filp, int uid, unsigned int group,
+			  __u32 data)
 {
 	struct kkuc_reg *reg;