mb/google/poppy/rammus: rework method get_wifi_sar_cbfs_filename

The return statement at the end of the method is never reached. Remove
it. Also while at it, assign the return value of variant_board_sku()
to ski_id while the variable declaration and make it const.

Signed-off-by: Yuchen He <yuchenhe126@gmail.com>
Change-Id: If05df8934f68ffec9ad21c88394055f71d618133
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73867
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Felix Singer <felixsinger@posteo.net>

src/mainboard/google/poppy/variants/rammus/mainboard.c

@@ -33,13 +33,10 @@ const char *smbios_system_sku(void)
 
 const char *get_wifi_sar_cbfs_filename(void)
 {
-	uint32_t sku_id;
+	const uint32_t sku_id = variant_board_sku();
 
-	sku_id = variant_board_sku();
 	if (sku_id & 0x200)
 		return "wifi_sar-shyvana.hex";
 	else
 		return "wifi_sar-leona.hex";
-
-	return WIFI_SAR_CBFS_DEFAULT_FILENAME;
 }