LU-6142 mdc: include linux/idr.h for referenced code

LU-6142 mdc: include linux/idr.h for referenced code

Include the <linux/idr.h> header in files that references IDR
functionality.  Don't depend on its indirect inclusion elsewhere.

Lustre-change: https://review.whamcloud.com/43346
Lustre-commit: 3589a3141a4b9f94887b3ac5d6202233b06b8996

Test-Parameters: trivial
Fixes: 66172e3274ca ("LU-13238 ofd: add OFD access logs")
Fixes: d0423abc1adc ("LU-12506 changelog: support large number of MDT")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Icdd03e15d31eabc4a1363d1757fc4db7723ebbe5
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-on: https://review.whamcloud.com/44233
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>