usb: stm32: fix calculation of TX FIFO sizes

The RX FIFO size is in words, so needs to be subtracted from the total
memory size *after* it's divided by 4.

Fixes #70789.

Signed-off-by: Armin Brauns <armin.brauns@embedded-solutions.at>

drivers/usb/device/usb_dc_stm32.c

@@ -131,10 +131,10 @@ static const struct gpio_dt_spec ulpi_reset =
 #define TX_FIFO_NUM USB_NUM_BIDIR_ENDPOINTS
 
 /* We need a minimum size for RX FIFO */
-#define USB_FIFO_RX_MIN 160
+#define RX_FIFO_EP_WORDS 160
 
 /* 4-byte words TX FIFO */
-#define TX_FIFO_WORDS ((USB_RAM_SIZE - USB_FIFO_RX_MIN - 64) / 4)
+#define TX_FIFO_WORDS ((USB_RAM_SIZE - 64) / 4 - RX_FIFO_EP_WORDS)
 
 /* Allocate FIFO memory evenly between the TX FIFOs */
 /* except the first TX endpoint need only 64 bytes */
@@ -446,7 +446,7 @@ static int usb_dc_stm32_init(void)
 #else /* USB_OTG_FS */
 
 	/* TODO: make this dynamic (depending usage) */
-	HAL_PCDEx_SetRxFiFo(&usb_dc_stm32_state.pcd, USB_FIFO_RX_MIN);
+	HAL_PCDEx_SetRxFiFo(&usb_dc_stm32_state.pcd, RX_FIFO_EP_WORDS);
 	for (i = 0U; i < USB_NUM_BIDIR_ENDPOINTS; i++) {
 		if (i == 0) {
 			/* first endpoint need only 64 byte for EP_TYPE_CTRL */