video: fbdev: via: remove possibly unused variables

When CONFIG_PROC_FS is disabled, we get warnings about unused variables
as remove_proc_entry() evaluates to an empty macro.

drivers/video/fbdev/via/viafbdev.c: In function 'viafb_remove_proc':
drivers/video/fbdev/via/viafbdev.c:1635:4: error: unused variable 'iga2_entry' [-Werror=unused-variable]
drivers/video/fbdev/via/viafbdev.c:1634:4: error: unused variable 'iga1_entry' [-Werror=unused-variable]

These are easy to avoid by using the pointer from the structure.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>