revokefs: Use correct format string for a ssize_t

This fixes the build on ILP32 architectures such as i386 with the Meson
build system. The Autotools build system accidentally didn't build
revokefs with -Werror=format, because it sets the target-specific CFLAGS
for revokefs but does not include the $(AM_CFLAGS) in them.

Fixes: aeecbb7 "revokefs: Split out the writing part from the fuse implementation"
Signed-off-by: Simon McVittie <[email protected]>

revokefs/writer.c

@@ -886,7 +886,7 @@ do_writer (int basefd_arg,
 
  if (response_data_size < 0 || response_data_size > MAX_DATA_SIZE)
  {
- g_printerr ("Invalid response size %ld", response_data_size);
+ g_printerr ("Invalid response size %zd", response_data_size);
  exit (1);
  }