ACPI: NUMA: HMAT: fix a section mismatch

Commit cf8741ac ("ACPI: NUMA: HMAT: Register "soft reserved"
memory as an "hmem" device") introduced a linker warning,

WARNING: vmlinux.o(.text+0x64ec3c): Section mismatch in reference from
the function hmat_register_target() to the function
.init.text:hmat_register_target_devices()

The function hmat_register_target() references the function __init
hmat_register_target_devices().

Since hmat_register_target() is also called from hmat_callback(), and
then register_hotmemory_notifier(), where it should not be freed when
hmat_init() is done, it indicates that the __init annotation of
hmat_register_target_devices() is incorrect.

Fixes: cf8741ac

 ("ACPI: NUMA: HMAT: Register "soft reserved" memory as an "hmem" device")
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>