libfrog: make platform_set_blocksize exit on fatal failure

libfrog: make platform_set_blocksize exit on fatal failure

platform_set_blocksize has a fatal argument that is currently only
used to change the printed message.  Make it actually fatal similar to
other libfrog platform helpers to simplify the caller.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>