power: qpnp-qg: Allow signed values for Rconn property

Currently, Rconn value is read as unsigned, but
now signed value can be added, typecast it before
assigning it to variable.

Change-Id: If87adf2da724b5bbdef081018c59d52530c97f7b
Signed-off-by: Kavya Nunna <knunna@codeaurora.org>