usb: st_usbfs_v2: allow unaligned buffers for st_usbfs_copy_from_pm()

The previous implementation of copy_from_pm assumed the destination buffer
was aligned on a 16-bit boundary. On M0/M0+ cores (stm32F0*, stm32L0*)
this causes a hard fault.
This implementation is from Kuldeep Dhaka's tree; it does a 16-bit copy
only if the destination buffer is aligned, otherwise a bytewise copy.

Fixes GH issues #401, #461

lib/stm32/st_usbfs_v2.c

@@ -79,15 +79,23 @@ void st_usbfs_copy_to_pm(volatile void *vPM, const void *buf, uint16_t len)
  */
 void st_usbfs_copy_from_pm(void *buf, const volatile void *vPM, uint16_t len)
 {
-	uint16_t *lbuf = buf;
 	const volatile uint16_t *PM = vPM;
 	uint8_t odd = len & 1;
+	len >>= 1;
 
-	for (len >>= 1; len; PM++, lbuf++, len--) {
+	if (((uintptr_t) buf) & 0x01) {
-		*lbuf = *PM;
+		for (; len; PM++, len--) {
+			uint16_t value = *PM;
+			*(uint8_t *) buf++ = value;
+			*(uint8_t *) buf++ = value >> 8;
+		}
+	} else {
+		for (; len; PM++, buf += 2, len--) {
+			*(uint16_t *) buf = *PM;
+		}
 	}
 
 	if (odd) {
-		*(uint8_t *) lbuf = *(uint8_t *) PM;
+		*(uint8_t *) buf = *(uint8_t *) PM;
 	}
 }