extmod/vfs_blockdev: Support bool return from Python read/write blocks.

Commit f4ab9d9247 inadvertently broke some
Python block devices, for example esp32 and stm32 SDCard classes.  Those
classes return a bool from their `readblocks` and `writeblocks` methods
instead of an integer errno code.  With that change, both `False` and
`True` return values are now be interpreted as non-zero and hence the block
device call fails.

The fix in this commit is to allow a bool and explicitly convert `True` to
0 and `False` to `-MP_EIO`.

Signed-off-by: Damien George <damien@micropython.org>

extmod/vfs_blockdev.c

@@ -58,6 +58,13 @@ static int mp_vfs_blockdev_call_rw(mp_obj_t *args, size_t block_num, size_t bloc
     if (ret == mp_const_none) {
         return 0;
     } else {
+        // Some block devices return a bool indicating success, so
+        // convert those to an errno integer code.
+        if (ret == mp_const_true) {
+            return 0;
+        } else if (ret == mp_const_false) {
+            return -MP_EIO;
+        }
         // Block device functions are expected to return 0 on success
         // and negative integer on errors. Check for positive integer
         // results as some callers (i.e. littlefs) will produce corrupt