Documentation: dt: update ti,am33xx-hsmmc swakeup workaround

Before 5b83b223 the driver was hard coding the wakeup irq to
be active low. The generic pm wakeirq does not override the active
high/low parameter, hence it must be specified correctly in the
device tree.
Mind that SDIO IRQ is active low as defined in the SDIO specification

Signed-off-by: Andreas Fenkart <afenkart@gmail.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>