On LS2088A-RDB board, if the spi-fsl-dspi driver is built as module
then its probe fails with the following warning:

[   10.471363] couldn't get idr
[   10.471381] WARNING: CPU: 4 PID: 488 at drivers/spi/spi.c:2689 spi_register_controller+0x73c/0x8d0
...
[   10.471651] fsl-dspi 2100000.spi: Problem registering DSPI ctlr
[   10.471708] fsl-dspi: probe of 2100000.spi failed with error -16

Reason for the failure is that bus-num property is set for dspi node.
However, bus-num property is not set for the qspi node. If probe for
spi-fsl-qspi happens first then id 0 is dynamically allocated to it.
Call to spi_register_controller() from spi-fsl-dspi driver then fails.
Since commit 29d2daf2 ("spi: spi-fsl-dspi: Make bus-num property
optional") bus-num property is optional. Remove bus-num property from
dspi node to fix the issue.
Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>