kobject: make get_ktype() take a const pointer

get_ktype() does not modify the structure passed to it, so mark the
parameter as being const to allow other const structures to be passed to
it in the future.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20221021072310.3931690-1-gregkh@linuxfoundation.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>