Correct the doxygen warnings for RingProfile

re #7776
Deal with cpp check related to RingProfile

There were 3 groups of warnings:

1 - scope variable of xpos, diffx, distance in the line 563. This warning
was ignored, as putting these variables inside the scope (inside the loop)
would be worse.
2 - unsignedLessThanZero - variable i in line 276. Corrected
3 - unreadVariable - x\y\zOutside unused line 324. Corrected.

re #7776