staging: fbtft: fbtft-core: Use '%zu' to print 'size_t' format

When building for ARM64 the following build warning is seen:

drivers/staging/fbtft/fbtft-core.c:1004:4: warning: format '%d' expects argument of type 'int', but argument 3 has type 'size_t' [-Wformat=]

Use '%zu' to print 'size_t' format.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fbtft-core.c

@@ -1000,7 +1000,7 @@ int fbtft_register_framebuffer(struct fb_info *fb_info)
 	fbtft_sysfs_init(par);
 
 	if (par->txbuf.buf)
-		sprintf(text1, ", %d KiB %sbuffer memory",
+		sprintf(text1, ", %zu KiB %sbuffer memory",
 			par->txbuf.len >> 10, par->txbuf.dma ? "DMA " : "");
 	if (spi)
 		sprintf(text2, ", spi%d.%d at %d MHz", spi->master->bus_num,