leds: qpnp-leds: correct bugs in driver probe

There are 4 errors during the probe of leds-qpnp:
1) dev_kzalloc should only be called when num_leds > 0
2) led->num_leds is only set for the first child led node
3) return path does not unregister leds in all cases
4) cleanup for more than 1 led in probe fails

These must be corrected.

CRs-fixed: 422575
Change-Id: Ie0c4f3d8ee12dfabe48c1f78162941aedb5dbb52
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>