Documentation/features-refresh.sh: Only sed the beginning "arch" of ARCH_DIR

It should only sed the beginning "arch" of ARCH_DIR in features-refresh.sh,
otherwise loongarch is recognized as loong, that is not what we want.

Fixes: be99f610a110 ("Documentation/features: Add script that refreshes the arch support status files in place")
Signed-off-by: Tiezhu Yang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/features/scripts/features-refresh.sh

···
 	echo "    |         arch |status|" >> $T_FILE
 	echo "    -----------------------" >> $T_FILE
 	for ARCH_DIR in arch/*/; do
-		ARCH=$(echo $ARCH_DIR | sed -e 's/arch//g' | sed -e 's/\///g')
+		ARCH=$(echo $ARCH_DIR | sed -e 's/^arch//g' | sed -e 's/\///g')
 		K_FILES=$(find $ARCH_DIR -name "Kconfig*")
 		K_GREP=$(grep "$K" $K_FILES)
 		#