btrfs: qgroup: delete unnecessary check in btrfs_qgroup_check_inherit()

This check "if (inherit->num_qgroups > PAGE_SIZE)" is confusing and
unnecessary.

The problem with the check is that static checkers flag it as a
potential mixup of between units of bytes vs number of elements.
Fortunately, the check can safely be deleted because the next check is
correct and applies an even stricter limit:

	if (size != struct_size(inherit, qgroups, inherit->num_qgroups))
		return -EINVAL;

The "inherit" struct ends in a variable array of __u64 and
"inherit->num_qgroups" is the number of elements in the array.  At the
start of the function we check that:

	if (size < sizeof(*inherit) || size > PAGE_SIZE)
		return -EINVAL;

Thus, since we verify that the whole struct fits within one page, that
means that the number of elements in the inherit->qgroups[] array must
be less than PAGE_SIZE.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>