staging: nvec: Fix incorrect type of i2c address

The i2c address is unsigned according to the dt-bindings.
Fix sparse issue (-Wtypesign):

  drivers/staging/nvec/nvec.c:781:35: warning: incorrect type in argument 3 (different signedness)
  drivers/staging/nvec/nvec.c:781:35:    expected unsigned int [usertype] *out_value
  drivers/staging/nvec/nvec.c:781:35:    got int *<noident>

Signed-off-by: Franck Demathieu <fdemathieu@gmail.com>
Acked-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>