LU-16684 utils: reset buf_len in print_out_devices()

LU-16684 utils: reset buf_len in print_out_devices()

so that print_out_devices() doesn't hit false buffer overflow
leading to missing devices in lctl device_list output.

Fixes: ba0d5ffc1c ("LU-9680 utils: new llapi_param_display_value().")
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Ia0ebbd0150651d7c631348201c26ea8b3d1ff704
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50475
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>