idr: Fix idr_alloc_u32 on 32-bit systems

idr: Fix idr_alloc_u32 on 32-bit systems

BugLink: https://bugs.launchpad.net/bugs/1855787
[ Upstream commit b7e9728f3d7fc5c5c8508d99f1675212af5cfd49 ]

Attempting to allocate an entry at 0xffffffff when one is already
present would succeed in allocating one at 2^32, which would confuse
everything.  Return -ENOSPC in this case, as expected.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>