Input: atlas - check ACPI_COMPANION() against NULL

Input: atlas - check ACPI_COMPANION() against NULL

Every platform driver can be forced to match a device that doesn't match
its list of device IDs because of device_match_driver_override(), so
platform drivers that rely on the existence of a device's ACPI companion
object need to verify its presence.

Accordingly, add a requisite ACPI_COMPANION() check against NULL to the
atlas_btns driver.

Fixes: b8303880b641 ("Input: atlas - convert ACPI driver to a platform one")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/8696590.T7Z3S40VBb@rafael.j.wysocki
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>