nilfs2: fix missing cleanup of gc cache on error cases

This fixes an -rc1 regression brought by the commit:
1cf58fa8 ("nilfs2: shorten freeze
period due to GC in write operation v3").

Although the patch moved out a function call of
nilfs_ioctl_move_blocks() to nilfs_ioctl_clean_segments() from
nilfs_ioctl_prepare_clean_segments(), it didn't move corresponding
cleanup job needed for the error case.

This will move the missing cleanup job to the destination function.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Acked-by: Jiro SEKIBA <jir@unicus.jp>