kbuild: mkcompile_h: trivial cleanups

UTS_TRUNCATTE is simpler this way, and now editors idetify this as a
shell script.
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Acked-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/mkcompile_h

+#!/bin/sh
+
 TARGET=$1
 ARCH=$2
 SMP=$3
@@ -50,7 +52,7 @@ UTS_VERSION="$UTS_VERSION $CONFIG_FLAGS $TIMESTAMP"
 # Truncate to maximum length
 
 UTS_LEN=64
-UTS_TRUNCATE="sed -e s/\(.\{1,$UTS_LEN\}\).*/\1/"
+UTS_TRUNCATE="cut -b -$UTS_LEN"
 
 # Generate a temporary compile.h