gpio: mcp23s08: Bug fix of SPI device tree registration.
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.
Cc: stable@vger.kernel.org Signed-off-by: Michael Welling <mwelling@ieee.org> Acked-by: Peter Korsgaard <peter@korsgaard.com> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>