cmd: sf: Fix sf probe crash

Handle the return value of spi_flash_probe_bus_cs() to avoid sf probe
crashes.

Link: https://lore.kernel.org/all/20240104114619.280513-1-o451686892@gmail.com


Signed-off-by: Weizhao Ouyang <o451686892@gmail.com>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>
Acked-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>