init.sh: tidy up xbmk_child_exec()

make the command style more consistent, for example
relying on x_ inside a subshell to print the command
and arguments if a command failed.

this is a good style, and i'll probably use it in other
places on lbmk.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/init.sh

@@ -204,8 +204,8 @@ xbmk_child_exec()
 {
 	xbmk_rval=0
 	( x_ ./mk "$@" ) || xbmk_rval=1
-	rm -Rf "$xbmklocal" "$xbmktmp" || xbmk_rval=1
-	rm -f lock || xbmk_rval=1
+	( x_ rm -Rf "$xbmklocal" "$xbmktmp" ) || xbmk_rval=1
+	( x_ rm -f lock ) || xbmk_rval=1
 	exit $xbmk_rval
 }