power: qpnp-smbcharger: update iusb only at beginning of charging

Since AICL result cannot be larger than maximum input current
setting, do not update maximum input current again when it is
already determined. If not, maximum input current could be
lower by a short input voltage drop and the AICL result never
goes back to the higher value.

Bug: 24372404

Change-Id: I20ef13f621d6b8cb95729f9d582639f7f6ab4b35
Signed-off-by: choongryeol.lee <choongryeol.lee@lge.com>