power: qpnp-fg-gen3: allow negative Rconn configuration

In some cases, to offset the battery resistance which may be high
because of battery profile characterization and hardware layout,
negative connector resistance (Rconn) should be specified. Allow
configuring it.

Change-Id: Ief64ac13ba0a384a599fe6fffdbc0d093180d0b8
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>