fault-injection: fix failcmd.sh warning

"fault-injection: add tool to run command with failslab or
fail_page_alloc" added tools/testing/fault-injection/failcmd.sh to make it
easier to inject slab/page allocation failures by fault injection.

failcmd.sh prints the following warning when running with arguments
for command.

# ./failcmd.sh echo aaa
failcmd.sh: line 209: [: echo: binary operator expected
aaa

This warning is caused by an improper check whether at least one
parameter is left after parsing command options.

Fix it by testing the length of $1 instead of $@

Signed-off-by: Akinobu Mita <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

tools/testing/fault-injection/failcmd.sh

···
 	esac
 done
 
-[ -z "$@" ] && exit 0
+[ -z "$1" ] && exit 0
 
 echo $oom_kill_allocating_task > /proc/sys/vm/oom_kill_allocating_task
 echo $task_filter > $FAULTATTR/task-filter