leds: qpnp-wled: change the initcall level for qpnp-wled driver

Change the initcall level of qpnp-wled driver from module_init()
to subsys_initcall() so that the wled device can be available
earlier. This helps the clients to access the wled device earlier
without a probe deferral.

Change-Id: I3f0b409b2d42b2fc082de2c9f0f37fa30dfe7e9c
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>