board/ti/am62x-sk/readme.txt: fix defconfig target

am62x_sk_defconfig should be ti_am62x_sk_defconfig

Signed-off-by: Adam Duskett <adam.duskett@amarulasolutions.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

board/ti/am62x-sk/readme.txt

@@ -11,7 +11,7 @@ How to Build
 
 Select the default configuration for the target:
 
-$ make am62x_sk_defconfig
+$ make ti_am62x_sk_defconfig
 
 Optional: modify the configuration: