hw/usb/hcd-dwc2: Handle invalid address access in read and write functions

This commit modifies the dwc2_hsotg_read() and dwc2_hsotg_write() functions
to handle invalid address access gracefully. Instead of using
g_assert_not_reached(), which causes the program to abort, the functions
now log an error message and return a default value for reads or do
nothing for writes.

This change prevents the program from aborting and provides clear log
messages indicating when an invalid memory address is accessed.

Reproducer:
cat << EOF | qemu-system-aarch64 -display none \
-machine accel=qtest, -m 512M -machine raspi2b -m 1G -nodefaults \
-usb -drive file=null-co://,if=none,format=raw,id=disk0 -device \
usb-storage,port=1,drive=disk0 -qtest stdio
readl 0x3f980dfb
EOF

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
Reviewed-by: Paul Zimmerman <pauldzim@gmail.com>
Message-id: 20240618135610.3109175-1-zheyuma97@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/usb/hcd-dwc2.c

@@ -1128,7 +1128,10 @@ static uint64_t dwc2_hsotg_read(void *ptr, hwaddr addr, unsigned size)
         val = dwc2_pcgreg_read(ptr, addr, (addr - HSOTG_REG(0xe00)) >> 2, size);
         break;
     default:
-        g_assert_not_reached();
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Bad offset 0x%"HWADDR_PRIx"\n",
+                      __func__, addr);
+        val = 0;
+        break;
     }
 
     return val;
@@ -1160,7 +1163,9 @@ static void dwc2_hsotg_write(void *ptr, hwaddr addr, uint64_t val,
         dwc2_pcgreg_write(ptr, addr, (addr - HSOTG_REG(0xe00)) >> 2, val, size);
         break;
     default:
-        g_assert_not_reached();
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Bad offset 0x%"HWADDR_PRIx"\n",
+                      __func__, addr);
+        break;
     }
 }