fix(dracut-install): memory leak

"Error: RESOURCE_LEAK (CWE-772):
src/install/dracut-install.c:1135: alloc_fn: Storage is returned from allocation function ""strv_split"".
src/install/dracut-install.c:1135: var_assign: Assigning: ""firmwaredirs"" = storage returned from ""strv_split(optarg, "":"")"".
src/install/dracut-install.c:1135: overwrite_var: Overwriting ""firmwaredirs"" in ""firmwaredirs = strv_split(optarg, "":"")"" leaks the storage that ""firmwaredirs"" points to.
 1133|                           break;
 1134|                   case ARG_FIRMWAREDIRS:
 1135|->                         firmwaredirs = strv_split(optarg, "":"");
 1136|                           break;
 1137|                   case 'f':"

src/install/dracut-install.c

@@ -1140,6 +1140,7 @@ static int parse_argv(int argc, char *argv[])
                         kerneldir = optarg;
                         break;
                 case ARG_FIRMWAREDIRS:
+                        strv_free(firmwaredirs);
                         firmwaredirs = strv_split(optarg, ":");
                         break;
                 case 'f':