platform/x86: intel-vbtn: Fix return value check in check_acpi_dev()

In the function check_acpi_dev(), if it fails to create
platform device, the return value is ERR_PTR() or NULL.
Thus it must use IS_ERR_OR_NULL() to check return value.

Fixes: 332e0812 ("intel-vbtn: new driver for Intel Virtual Button")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Lu Wei <luwei32@huawei.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>