I hope you realize that in order to have data from an axi slave to a 8 bit register, the 8 bit register must also have an axi wrapper. That axi wrapper must act as an axi master. Since you already have the slave you need to write the axi master RTL.
I hope you realize that in order to have data from an axi slave to a 8 bit register, the 8 bit register must also have an axi wrapper. That axi wrapper must act as an axi master. Since you already have the slave you need to write the axi master RTL.