power: pm8921-charger: Correct USB online reporting

When a USB charger is first connected to the device
the USB driver determines the maximum available charge
current. If the USB driver determines that a wall charger
is connected there is a possiblity of the USB power
supply type to falsely be reported as online.

Fix this by only reporting the USB online state if the
targeted maximum USB current is less than 500 mA. This
means that there was no wall charger ever connected and
AICL will not be utilized.

Change-Id: I0b14da273fbc2a94fe49250fa800a2136c3f09a2
Signed-off-by: David Keitel <dkeitel@codeaurora.org>