SDCard: add missing import

internal_filesystem/lib/mpos/sdcard.py

@@ -21,14 +21,15 @@ class SDCardManager:
             print(f"SD card mounted successfully at {mount_point}")
             return True
         except OSError as e:
-            errno = -1
+            error_nr = -1
             try:
-                errno = e.errno
+                error_nr = e.errno
             except NameError as we:
                 print("Got this weird (sporadic) \"NameError: name 'errno' isn't defined\" again when parsing OSError: {we}")
                 print(f"Original exception: {e}")
                 print(dir(e))
-            if errno == errno.EPERM:  # EPERM is 1, meaning already mounted
+            import errno
+            if error_nr == errno.EPERM:  # EPERM is 1, meaning already mounted
                 print(f"Got mount error {e} which means already mounted.")
                 return True
             else: