MIPS: Alchemy: Fix an out-of-bound access in db1550_dev_setup()

[ Upstream commit 3c1e5abcda64bed0c7bffa65af2316995f269a61 ]

When calling spi_register_board_info(),

Fixes: f869d42e ("MIPS: Alchemy: Improved DB1550 support, with audio and serial busses.")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>