Previously, the caller checked ATTN_LED() or PWR_LED() to see whether the
slot has indicators before setting the indicator state.  That clutters the
caller unnecessarily, so this moves the test inside the callees.  The test
may not even be necessary; per spec it should be harmless to try to turn on
a non-existent LED.  But checking first does avoid unnecessary hotplug
commands.

No functional change.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>