ARM: dts: imx6qdl-sr-som-brcm: rename sdio clock

The SDIO clock is really the Broadcom clock.  Rename it as such.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>