ACPI: sysfs: Unify pattern of memory allocations

Use the form of foo = kmalloc(sizeof(*foo)) everywhere in order to
unify pattern of memory allocations.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>