fw_printenv: Fix crash due to incorrect size for malloc'ed string.

Using sizeof gives the size of the pointer only, not the string. This
could easily lead to crashes when using -l argument.
Signed-off-by: NKristian Amlie <kristian.amlie@northern.tech>

tools/env/fw_env_main.c

@@ -239,7 +239,7 @@ int main(int argc, char *argv[])
 	argv += optind;
 
 	if (env_opts.lockname) {
-		lockname = malloc(sizeof(env_opts.lockname) +
+		lockname = malloc(strlen(env_opts.lockname) +
 				sizeof(CMD_PRINTENV) + 10);
 		if (!lockname) {
 			fprintf(stderr, "Unable allocate memory");