leds: qpnp-wled: fix issues raised by static analyzer

Fix the issues raised by static analyzer:
1. Replace 'memcpy' with a member-wise copy of the strings array.
2. Remove comparison of unsigned values against 0.

Change-Id: I54153240faa236eb68bcceb8e64edd23704a245c
Signed-off-by: Himanshu Aggarwal <haggarwa@codeaurora.org>