ARM: dts: ls1021a: Update 'dspi' device node compatible string

Freescale DSPI driver has been updated and supports TCF interrupt type now.
In the new driver we choose the interrupt type according the compatible
string of the device node.
This patch update the compatible string of DSPI device node of LS1021A in
order to use the correct interrupt type.

Signed-off-by: Haikun Wang <haikun.wang@freescale.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>