cdch: fix FTDI latency-timer continuation callback

CFG_TUH_CDC_FTDI_LATENCY builds failed: the completion callback named
ftdi_process_config, which does not exist. Scope the result declaration
too -- a declaration right after a case label is invalid before C23, and
several ports build with -std=c99.

src/class/cdc/cdc_host.c

diff --git a/src/class/cdc/cdc_host.c b/src/class/cdc/cdc_host.c
index 7a979f6..e012139 100644
--- a/src/class/cdc/cdc_host.c
+++ b/src/class/cdc/cdc_host.c
@@ -1242,12 +1242,14 @@
 
     case CONFIG_FTDI_WRITE_LATENCY:
       #ifdef CFG_TUH_CDC_FTDI_LATENCY
-      int8_t result = ftdi_write_latency_timer(p_cdc, CFG_TUH_CDC_FTDI_LATENCY, ftdi_process_config,
-                                               CONFIG_FTDI_SIO_RESET);
-      TU_ASSERT(result != FTDI_FAIL);
-      if (result == FTDI_REQUESTED) {
-        break;
-      }// else FTDI_NOT_POSSIBLE => continue directly with next state
+      {
+        int8_t result = ftdi_write_latency_timer(p_cdc, CFG_TUH_CDC_FTDI_LATENCY, cdch_process_set_config,
+                                                 CONFIG_FTDI_SIO_RESET);
+        TU_ASSERT(result != FTDI_FAIL);
+        if (result == FTDI_REQUESTED) {
+          break;
+        }// else FTDI_NOT_POSSIBLE => continue directly with next state
+      }
       #endif
       TU_ATTR_FALLTHROUGH;