io_uring: fix types in io_recvmsg_multishot_overflow

io_uring: fix types in io_recvmsg_multishot_overflow

io_recvmsg_multishot_overflow had incorrect types on non x64 system.
But also it had an unnecessary INT_MAX check, which could just be done
by changing the type of the accumulator to int (also simplifying the
casts).

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: a8b38c4ce724 ("io_uring: support multishot in recvmsg")
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220715130252.610639-1-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>