dummyflasher.c: Fix memory leak on shutdown

emu_data *data is allocated in init function and needs
to be freed in shutdown function.

BUG=b:181803212
TEST=builds and ninja test

Change-Id: I36f76d84d3547d081c64857e06da23ee63cc5594
Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/52557
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>

dummyflasher.c

@@ -650,6 +650,7 @@ static int dummy_shutdown(void *data)
 		free(flashchip_contents);
 	}
 #endif
+	free(data);
 	return 0;
 }