smatch stuff: a couple unused assignments in ext4

Roel's fix got merged so now there are only two unused assignments left in ext4.

fs/ext4/extents.c +3578 ext4_ext_truncate warn: assignment to 'err' was never used fs/ext4/mballoc.c +2050 ext4_mb_regular_allocator warn: assignment to 'desc' was never used

I'm not sure what the fix should be.

BTW. I'm always trying to figure out the best way to report smatch issues. Let me know how I can improve the process.

regards,
dan carpenter