staging: fbtft: fix sparse warning

fix the following sparse warning:
 drivers/staging/fbtft/fbtft-io.c:74:29: warning: incorrect type in assignment
 (different base types) drivers/staging/fbtft/fbtft-io.c:74:29:    expected
 unsigned long long [unsigned] [long] [long long] [usertype] <noident>
 drivers/staging/fbtft/fbtft-io.c:74:29:    got restricted __be64 [usertype]
 <noident>
Signed-off-by: NJandy Gou <gouqingsong@goodix.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fbtft-io.c

@@ -71,7 +71,7 @@ int fbtft_write_spi_emulate_9(struct fbtft_par *par, void *buf, size_t len)
 			src++;
 		}
 		tmp |= ((*src & 0x0100) ? 1 : 0);
-		*(u64 *)dst = cpu_to_be64(tmp);
+		*(__be64 *)dst = cpu_to_be64(tmp);
 		dst += 8;
 		*dst++ = (u8)(*src++ & 0x00FF);
 		added++;