video: fbdev: sis: make const array specialtv static, reduces object code size

Don't populate the const array specialtv on the stack, instead make it
static.  Makes the object code smaller by over 1100 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
 179899	   7504	      0	 187403	  2dc0b	drivers/video/fbdev/sis/init301.o

After:
   text	   data	    bss	    dec	    hex	filename
 178720	   7568	      0	 186288	  2d7b0	drivers/video/fbdev/sis/init301.o

(gcc version 7.2.0, x86_64)

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Cc: Thomas Winischhofer <thomas@winischhofer.net>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>