iov_iter: Export import_ubuf()

Export import_ubuf() to be used in sound subsystem for generic memory
handling as Linus suggested.  It's used for constructing an iov_iter
of a single segment user-space copy for PCM data.

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/CAHk-=wh-mUL6mp4chAc6E_UjwpPLyCPRCJK+iB4ZMD2BqjwGHA@mail.gmail.com
Link: https://lore.kernel.org/r/20230815190136.8987-2-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

lib/iov_iter.c

@@ -1544,6 +1544,7 @@ int import_ubuf(int rw, void __user *buf, size_t len, struct iov_iter *i)
 	iov_iter_ubuf(i, rw, buf, len);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(import_ubuf);
 
 /**
  * iov_iter_restore() - Restore a &struct iov_iter to the same state as when