staging: fbtft: make const array gamma_par_mask static

Don't populate array gamma_par_mask on the stack but instead make it
static.  Makes the object code smaller by 148 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
   2993	   1104	      0	   4097	   1001	drivers/staging/fbtft/fb_st7789v.o

After:
   text	   data	    bss	    dec	    hex	filename
   2757	   1192	      0	   3949	    f6d	drivers/staging/fbtft/fb_st7789v.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fb_st7789v.c

@@ -189,7 +189,7 @@ static int set_gamma(struct fbtft_par *par, u32 *curves)
 	 * The masks are the same for both positive and negative voltage
 	 * gamma curves.
 	 */
-	const u8 gamma_par_mask[] = {
+	static const u8 gamma_par_mask[] = {
 		0xFF, /* V63[3:0], V0[3:0]*/
 		0x3F, /* V1[5:0] */
 		0x3F, /* V2[5:0] */