sh: sh7786: Fix last GPIO index

A careless look at the code shows that the last entry in the
pinmux_gpios seems to be GPIO_FN_FSE. However, entries are ordered by
the GPIO number, as the PINMUX_GPIO macro is expended to an indexed
array initializer. The last entry in the array is thus GPIO_FN_IRL4. Set
the pinmux_info last_gpio field accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>