boards: amlogic: khadas-vim: Typo fixup

Khadas VIM is an Open Source DIY Box manufactured by Shenzhen Wesion NOT 'Tomato'

The fix was provided by Khadas Team member 'numbqq'.
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>

board/amlogic/khadas-vim/README

 U-Boot for Khadas VIM
 =======================
 
-Khadas VIM is an Open Source DIY Box manufactured by Shenzhen Tomato
+Khadas VIM is an Open Source DIY Box manufactured by Shenzhen Wesion
 Technology Co., Ltd with the following specifications:
 
  - Amlogic S905x ARM Cortex-A53 quad-core SoC @ 2GHz