ANDROID: AVB: Fix linter errors.

Various other kernel trees complained about style problems with
dm-verity-avb.c, specifically some lines being wider than 80
characters and spaces being used instead of tabs. With these changes
checkpatch.pl is happy:

 $ scripts/checkpatch.pl --file drivers/md/dm-verity-avb.c
 total: 0 errors, 0 warnings, 229 lines checked

 drivers/md/dm-verity-avb.c has no obvious style problems and is ready for submission.

Bug: None
Test: Compiles.
Change-Id: I08913adf61c5bf2b0f78f7d9e18dbe93feaba9f7
Signed-off-by: David Zeuthen <zeuthen@google.com>