Update directories for new name of TF-A directories

The TF-A URL was updated, as a result the name of the
directory changed as part of the new git URL and not
all the referenced directories were updated.

Fixes: 0ec0207fe07 ("Update the ARM trusted firmware git URL")
Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
diff --git a/board/rockchip/evb_rk3399/README b/board/rockchip/evb_rk3399/README
index c7caf17..de9509e 100644
--- a/board/rockchip/evb_rk3399/README
+++ b/board/rockchip/evb_rk3399/README
@@ -39,7 +39,7 @@
 Compile ATF
 ===========
 
-  > cd arm-trusted-firmware
+  > cd trusted-firmware-a
   > make realclean
   > make CROSS_COMPILE=aarch64-linux-gnu- PLAT=rk3399 bl31
 
@@ -91,7 +91,7 @@
 Package the image for Rockchip miniloader(option 2)
 ------------------------------------------
   > cd ..
-  > cp arm-trusted-firmware/build/rk3399/release/bl31.elf rkbin/rk33
+  > cp trusted-firmware-a/build/rk3399/release/bl31.elf rkbin/rk33
   > ./rkbin/tools/trust_merger rkbin/tools/RK3399TRUST.ini
   > ./rkbin/tools/loaderimage --pack --uboot u-boot/u-boot-dtb.bin uboot.img