sandbox: compatibility of os_get_filesize()

U-Boot define loff_t as long long. But the header
/usr/include/linux/types.h may not define it.
This has lead to a build error on Alpine Linux.

So let's use long long instead of loff_t for
the size parameter of function os_get_filesize().

Reported-by: Milan P. Stanić <mps@arvanta.net>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Tested-by: Milan P. Stanić <mps@arvanta.net>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/os.h b/include/os.h
index 4cbcbd9..10e198c 100644
--- a/include/os.h
+++ b/include/os.h
@@ -266,7 +266,7 @@
  * @size:	size of file is returned if no error
  * Return:	0 on success or -1 if an error ocurred
  */
-int os_get_filesize(const char *fname, loff_t *size);
+int os_get_filesize(const char *fname, long long *size);
 
 /**
  * os_putc() - write a character to the controlling OS terminal