pinctrl: exynos: Mark exynos_irq_demux_eint as inline

The exynos_irq_demux_eint utility function is used in chained IRQ
handler for EINT16-31 to handle multiplexed interrupts. Inlining it
should improve the performance a bit.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>