PNP: Remove pnp_alloc()

The kernel will complain anyway if it runs out of memory, so it is
not necessary to print an extra error message when that happens and
kzalloc() can be called directly instead of pnp_alloc() which then
becomes redundant and can be dropped.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>