tools:testing/selftests: fix typo in futex/README

Correct typo in tools/testing/selftests/futex/README.

Signed-off-by: Wei Jiangang <weijg.fnst@cn.fujitsu.com>
Acked-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

Author: Wei Jiangang

tools/testing/selftests/futex/README

@@ -27,7 +27,7 @@ o The build system shall remain as simple as possible, avoiding any archive or
 o Where possible, any helper functions or other package-wide code shall be
   implemented in header files, avoiding the need to compile intermediate object
   files.
-o External dependendencies shall remain as minimal as possible. Currently gcc
+o External dependencies shall remain as minimal as possible. Currently gcc
   and glibc are the only dependencies.
 o Tests return 0 for success and < 0 for failure.