env: Always use char for default_environment

Sometimes we use uchar and sometimes char for the default environment
array. By always using char, we can get rid of some explicit casts.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/env_default.h

@@ -20,9 +20,9 @@ env_t embedded_environment __UBOOT_ENV_SECTION__(environment) = {
 #elif defined(DEFAULT_ENV_INSTANCE_STATIC)
 static char default_environment[] = {
 #elif defined(DEFAULT_ENV_IS_RW)
-uchar default_environment[] = {
+char default_environment[] = {
 #else
-const uchar default_environment[] = {
+const char default_environment[] = {
 #endif
 #ifndef CONFIG_USE_DEFAULT_ENV_FILE
 #ifdef	CONFIG_ENV_CALLBACK_LIST_DEFAULT