gpio: mcp23s08: Bug fix of SPI device tree registration.

gpio: mcp23s08: Bug fix of SPI device tree registration.

commit 99e4b98dbe3ad1fe38a74d12c3b8d44a55930de4 upstream.

The chips variable needs to be incremented for each chip that is
found in the spi_present_mask when registering via device tree.
Without this and the checking a negative index is passed to the
data->chip array in a subsequent loop.

Signed-off-by: Michael Welling <mwelling@ieee.org>
Acked-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>