USB: ULPI: clean a mixup of return types

Clean a mixup between u32 and int as a return type
for functions returning error values.
Use int as it is native (and widely used) return type.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/usb/ulpi.h b/include/usb/ulpi.h
index dc78a59..802f077 100644
--- a/include/usb/ulpi.h
+++ b/include/usb/ulpi.h
@@ -108,7 +108,7 @@
  *
  * returns 0 on success, ULPI_ERROR on failure.
  */
-u32 ulpi_write(u32 ulpi_viewport, u8 *reg, u32 value);
+int ulpi_write(u32 ulpi_viewport, u8 *reg, u32 value);
 
 /*
  * Read the ULPI PHY register content via the viewport.