agp/via: Remove unused variable 'current_size'

Fix the compiler warning

  drivers/char/agp/via-agp.c: In function 'via_configure_agp3':
  drivers/char/agp/via-agp.c:131:35: warning: variable 'current_size' set but not used [-Wunused-but-set-variable]
    131 |         struct aper_size_info_16 *current_size;

by removing the variable.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20211201114645.15384-8-tzimmermann@suse.de