test/vsock: remove vsock_perf executable on make clean

We forgot to add vsock_perf to the rm command in the `clean`
target, so now we have a left over after `make clean` in
tools/testing/vsock.

Fixes: 8abbffd ("test/vsock: vsock_perf utility")
Cc: AVKrasnov@sberdevices.ru
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Simon Horman <horms@kernel.org> # build-tested
Link: https://lore.kernel.org/r/20230803085454.30897-1-sgarzare@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: stefano-garzarella

tools/testing/vsock/Makefile

@@ -8,5 +8,5 @@ vsock_perf: vsock_perf.o
 CFLAGS += -g -O2 -Werror -Wall -I. -I../../include -I../../../usr/include -Wno-pointer-sign -fno-strict-overflow -fno-strict-aliasing -fno-common -MMD -U_FORTIFY_SOURCE -D_GNU_SOURCE
 .PHONY: all test clean
 clean:
-	${RM} *.o *.d vsock_test vsock_diag_test
+	${RM} *.o *.d vsock_test vsock_diag_test vsock_perf
 -include *.d