fix a typo error in docs/platform/sifive_fu540.md
Signed-off-by: Yuan Li <dskwelmcy@163.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
The HiFive Unleashed device tree(DT) is merged in Linux v5.2 release. This
DT (device tree) is not backward compatible with the DT passed from FSBL.
-To use Linux v5.2 (or higher, the pre-built DTB (DT binary) from Linux v5.2
+To use Linux v5.2 (or higher), the pre-built DTB (DT binary) from Linux v5.2
(or higher) should be used to build SiFive FU540 OpenSBI binaries by using
the compile time option *FW_FDT_PATH*.