lls: mark max_order as unsigned short

The value is within 0 and 32.

Remove an `array subscript is below array bounds` warning.

libavutil/lls.c

@@ -48,7 +48,7 @@ void avpriv_update_lls(LLSModel *m, double *var, double decay)
     }
 }
 
-void avpriv_solve_lls(LLSModel *m, double threshold, int min_order)
+void avpriv_solve_lls(LLSModel *m, double threshold, unsigned short min_order)
 {
     int i, j, k;
     double (*factor)[MAX_VARS + 1] = (void *) &m->covariance[1][0];

libavutil/lls.h

@@ -39,7 +39,7 @@ typedef struct LLSModel {
 
 void avpriv_init_lls(LLSModel *m, int indep_count);
 void avpriv_update_lls(LLSModel *m, double *param, double decay);
-void avpriv_solve_lls(LLSModel *m, double threshold, int min_order);
+void avpriv_solve_lls(LLSModel *m, double threshold, unsigned short min_order);
 double avpriv_evaluate_lls(LLSModel *m, double *param, int order);
 
 #ifndef FF_API_LLS_PRIVATE