This was supposed to happen in 9efa1f8b ("ARM: psci: wire in smc command
help") along with some other changes. After rebases, the other changes
remained but this one was lost.. Do this right this time and specify the
appropriate BAREBOX_CMD_HELP.

Fixes: 9efa1f8b ("ARM: psci: wire in smc command help")
Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>