leds: qpnp-flash-v2: Return zero when parsing optional DT parameters fails

While parsing optional DT properties in the helper functions,
return 0 at the end of the function to ensure that there is not
an actual error.

While at it, print rc value when qpnp_flash_led_parse_common_dt()
fails.

Change-Id: I8f5ffddcd7794e667a7e860abd1b2bbc5b7b05dc
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>