acpi/pcihp.c: Rewrite acpi_pcihp_get_bsel using object_property_get_int

acpi_pcihp_get_bsel implements functionality of object_property_get_int for
specific property named ACPI_PCIHP_PROP_BSEL, but fails to decrement object's
reference counter properly. Rewriting it using generic object_property_get_int
serves two purposes: reducing code duplication and fixing memory leak.

Signed-off-by: Kirill Batuzov <batuzovk@ispras.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>