targets/qemu.mk: Fix skip-if-exist in swtpm_setup

Commit 46cad54 ("WiP flake.nix: make docker image usable for...")
added 'root' to the swtpm_setup call, but broke skip-if-exist because
the flags are supposed to be comma-separated.  swtpm_setup was ignoring
skip-if-exist and would fail if the config files exist.

Put a comma there so it works again.

Signed-off-by: Jonathon Hall <jonathon.hall@puri.sm>

targets/qemu.mk

@@ -16,7 +16,7 @@ endif
 
 ifeq "$(CONFIG_TPM2_TSS)" "y"
 SWTPM_TPMVER := --tpm2
-SWTPM_PRESETUP := swtpm_setup --create-config-files root skip-if-exist
+SWTPM_PRESETUP := swtpm_setup --create-config-files root,skip-if-exist
 else
 # TPM1 is the default
 SWTPM_TPMVER :=
@@ -111,4 +111,4 @@ run: $(TPMDIR)/.manufacture $(ROOT_DISK_IMG) $(MEMORY_SIZE_FILE) $(USB_FD_IMG)
 		$(QEMU_USB_TOKEN_DEV) \
 
 	stty sane
-	@echo
+	@echo