platform/x86: classmate-laptop: Add missing NULL pointer checks

In the Linux kernel, the following vulnerability has been resolved:

platform/x86: classmate-laptop: Add missing NULL pointer checks

In a few places in the Classmate laptop driver, code using the accel

object may run before that object's address is stored in the driver

data of the input device using it.

For example, cmpc_accel_sensitivity_store_v4() is the "show" method

of cmpc_accel_sensitivity_attr_v4 which is added in cmpc_accel_add_v4(),

before calling dev_set_drvdata() for inputdev->dev. If the sysfs

attribute is accessed prematurely, the dev_get_drvdata(&inputdev->dev)

call in in cmpc_accel_sensitivity_store_v4() returns NULL which

leads to a NULL pointer dereference going forward.

Moreover, sysfs attributes using the input device are added before

initializing that device by cmpc_add_acpi_notify_device() and if one

of them is accessed before running that function, a NULL pointer

dereference will occur.

For example, cmpc_accel_sensitivity_attr_v4 is added before calling

cmpc_add_acpi_notify_device() and if it is read prematurely, the

dev_get_drvdata(&acpi->dev) call in cmpc_accel_sensitivity_show_v4()

returns NULL which leads to a NULL pointer dereference going forward.

Fix this by adding NULL pointer checks in all of the relevant places.