ch32h417: make usbss_phy_cfg return void (unused read-back)

PVS-Studio (V530) flagged the discarded return value of usbss_phy_cfg at every
call site. The PHY back-door read-back is only a strobe; the value is never used
(matching the WCH EVT demo), so return void. PVS found no other issues in either
CH32H417 dcd.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QWhrtHjbSVMKcY68vxBwBm

src/portable/wch/dcd_ch32h417_usb30.c

diff --git a/src/portable/wch/dcd_ch32h417_usb30.c b/src/portable/wch/dcd_ch32h417_usb30.c
index e79e1e4..dcdc067 100644
--- a/src/portable/wch/dcd_ch32h417_usb30.c
+++ b/src/portable/wch/dcd_ch32h417_usb30.c
@@ -117,10 +117,10 @@
   }
 }
 
-static uint32_t usbss_phy_cfg(uint8_t addr, uint16_t data) {
+static void usbss_phy_cfg(uint8_t addr, uint16_t data) {
   USBSS_PHY_CFG_CR = (1u << 23) | ((uint32_t)addr << 16) | data;
   USBSS_PHY_CFG_DAT = 0x01;
-  return USBSS_PHY_CFG_DAT;
+  (void)USBSS_PHY_CFG_DAT; // read-back strobe; the returned value is not used
 }
 
 static void usbss_cfg_mod(void) {