ARM: dts: berlin: correct BG2Q's sdhci2 2nd clock

The optional 2nd clock is CLKID_SDIO. We removed CLK_IGNORE_UNUSED
from CLKID_SDIO's flag, so the sdhci2 doesn't work. This patch fixes
this issue by correcting the sdhci2's 2nd clock.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>