ARM: uniphier: fix README instruction for updating U-Boot via TFTP

Commit 3cb9abc9c5 ("ARM: uniphier: update U-Boot file names in
workflow") missed to update these two sentences.  Fix them now.

Replace u-boot-spl-dtb.bin and u-boot-dtb.img with u-boot-spl.bin
and u-boot.img, respectively.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

doc/README.uniphier

@@ -80,8 +80,8 @@ Write two files to the NAND device as follows:
  - u-boot.img         at the offset address 0x00010000
 
 If a TFTP server is available, the images can be easily updated.
-Just copy the u-boot-spl-dtb.bin and u-boot-dtb.img to the TFTP public
-directory, and then run the following command at the U-Boot command line:
+Just copy the u-boot-spl.bin and u-boot.img to the TFTP public directory,
+and then run the following command at the U-Boot command line:
 
   => run nandupdate
 
@@ -94,8 +94,8 @@ Write two files to the Boot partition 1 of the eMMC device as follows:
  - u-boot.img         at the offset address 0x00010000
 
 If a TFTP server is available, the images can be easily updated.
-Just copy the u-boot-spl-dtb.bin and u-boot-dtb.img to the TFTP public
-directory, and then run the following command at the U-Boot command line:
+Just copy the u-boot-spl.bin and u-boot.img to the TFTP public directory,
+and then run the following command at the U-Boot command line:
 
   => run emmcupdate