video: fbdev: aty: remove useless variable assignments in aty_var_to_crtc()

Value assigned to variable vdisplay at line 990 is overwritten
at line 1039 before it can be used. Also, variable assignment
at line 987 is the same as at line 1039. This makes such
variable assignments useless.

Remove these variable assignments and the code related.

Addresses-Covertity-ID: 1226900
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>