ceph: Amend checking to fix `make W=1` build breakage

In a few cases the code compares 32-bit value to a SIZE_MAX derived
constant which is much higher than that value on 64-bit platforms,
Clang, in particular, is not happy about this

fs/ceph/snap.c:377:10: error: result of comparison of constant 2305843009213693948 with expression of type 'u32' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
377 | if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
| ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix this by casting to size_t. Note, that possible replacement of SIZE_MAX
by U32_MAX may lead to the behaviour changes on the corner cases.

Signed-off-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Viacheslav Dubeyko <[e-mail]>
Signed-off-by: Ilya Dryomov <[e-mail]>

fs/ceph/snap.c

···
 
 	/* alloc new snap context */
 	err = -ENOMEM;
-	if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
+	if ((size_t)num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
 		goto fail;
 	snapc = ceph_create_snap_context(num, GFP_NOFS);
 	if (!snapc)