Update solvepnp.cpp

Clarified assert message for allowed PnP flags

modules/calib3d/src/solvepnp.cpp

@@ -94,7 +94,7 @@ bool cv::solvePnP( InputArray _opoints, InputArray _ipoints,
         return true;
     }
     else
-        CV_Error(CV_StsBadArg, "The flags argument must be one of CV_ITERATIVE or CV_EPNP");
+        CV_Error(CV_StsBadArg, "The flags argument must be one of CV_ITERATIVE, CV_P3P or CV_EPNP");
     return false;
 }