Staging: quickstart: Fix compilation warning on 64 bit arch

acpi_size is u32 or u64 depending on architecture. Cast it to
unsigned long and use %lu for printing.

This fix following build warning:
drivers/staging/quickstart/quickstart.c: In function ‘quickstart_acpi_ghid’:
drivers/staging/quickstart/quickstart.c:212:5: warning: format ‘%u’ expects argument of type ‘unsigned int’, but argument 3 has type ‘acpi_size’ [-Wformat]
Signed-off-by: Szymon Janc <szymon@janc.net.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/quickstart/quickstart.c

@@ -209,8 +209,9 @@ static int quickstart_acpi_ghid(struct quickstart_acpi *quickstart)
 		quickstart->button->id = *(uint64_t *)buffer.pointer;
 		break;
 	default:
-		pr_err("%s GHID method returned buffer of unexpected length %u\n",
-				quickstart->button->name, buffer.length);
+		pr_err("%s GHID method returned buffer of unexpected length %lu\n",
+				quickstart->button->name,
+				(unsigned long)buffer.length);
 		ret = -EINVAL;
 		break;
 	}