Relax inode usage estimate.

The current inode usage estimate applies a factor (1.04x) to account for
differences between the directory and file count and what mkfs.ext4
produces. Bump this to 1.06x to allow more leniency.

This increases bramble partition sizes by 32KB total.

Bug: 182365132
Test: manual test
Change-Id: I9ade82cb89422e31ae8c5df9fff31157e88278c5