ARM: dts: ls1021a: add "fsl,ls1021a-esdhc" compatible string to esdhc node

Commit a22950c8 (mmc: sdhci-of-esdhc: add quirk
SDHCI_QUIRK_BROKEN_TIMEOUT_VAL for ls1021a) added logic to the driver to
enable the broken timeout val quirk for ls1021a, but did not add the
corresponding compatible string to the device tree, so it didn't really
have any effect. Fix that.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>