soc/amd/picasso/smihandler: replace southbridge.c in comment with fch.c

southbridge.c was renamed and split into early_fch.c and fch.c.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Ie439e746fb3dfe9ec865481a76a09eab378242bb
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50458
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/amd/picasso/smihandler.c

@@ -226,7 +226,7 @@ int southbridge_io_trap_handler(int smif)
 
 /*
  * Table of functions supported in the SMI handler.  Note that SMI source setup
- * in southbridge.c is unrelated to this list.
+ * in fch.c is unrelated to this list.
  */
 static const struct smi_sources_t smi_sources[] = {
 	{ .type = SMITYPE_SMI_CMD_PORT, .handler = sb_apmc_smi_handler },