selftests: lib: fix prime_numbers module search and skip logic

prime_numbers modules search and skip logic removes the module instead
of searching for it. Fix it.

Signed-off-by: Shuah Khan (Samsung OSG) <[e-mail]>

tools/testing/selftests/lib/prime_numbers.sh

···
 # Kselftest framework requirement - SKIP code is 4.
 ksft_skip=4
 
-if ! /sbin/modprobe -q -r prime_numbers; then
+if ! /sbin/modprobe -q -n prime_numbers; then
 	echo "prime_numbers: module prime_numbers is not found [SKIP]"
 	exit $ksft_skip
 fi