selftests: Make the usage formatting consistent in kselftest_deps.sh

Add a colon in the "Optional" test usage message to ensure consistency
with the "Default" test usage message.

Signed-off-by: Gautam Menghani <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/kselftest_deps.sh

···
 echo "- Prints pass/fail dependency check for each tests/sub-test."
 echo "- Prints pass/fail targets and libraries."
 echo "- Default: runs dependency checks on all tests."
-echo "- Optional test name can be specified to check dependencies for it."
+echo "- Optional: test name can be specified to check dependencies for it."
 exit 1
 
 }