leds: qpnp-flash-v2: Return error code separately during current prediction

Currently when the maximum available current per flash switch is
calculated, it is returned along with the error code. This will
be confusing when a real error occurs. Fix this by returning
error code separately and obtain the current by passing it by
reference.

Change-Id: I9e2a3436e19cc37319316603e6dfa45241df8a49
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>