leds: qpnp-wled: Do not configure DTEST for PMI8998 v2.0

In PMI8998 v2.0, DTEST line is configured internally by the
hardware. Do not configure it explicitly in software.

CRs-Fixed: 2244974
Change-Id: I2b8150b5a97fd1851069ee0f1bbb45dd3d8cc048
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>