power: qpnp-charger: change max reported current from mA to uA

The power supply framework requires all units reported to be
in uA or uV.

Fix this by reporting the CURRENT_MAX property for the
dc power supply from mA to uA.

Change-Id: I34d1811344c0ccf55424f3593a1248bba21ec802
Signed-off-by: David Keitel <dkeitel@codeaurora.org>