xilinx_zynq: Add one variable to avoid overwriting QSPI bus

xilinx_zynq: Add one variable to avoid overwriting QSPI bus

commit 7b482bcf xilinx_zynq: added QSPI controller

Adds one QSPI controller, which has two spi buses, one is for
spi0, and another is for spi1. But when initializing the spi1
bus, "dev" has been overwrited by the ssi_create_slave_no_init() function,
so that qdev_get_child_bus() returns NULL and the last two m25p80 flashes
won't be attached to the spi1 bus, but to main-system-bus.

Here we add one variable to avoid overwriting.

Signed-off-by: Liming Wang <[email protected]>
Reviewed-by: Peter Crosthwaite <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>