LU-8066 libcfs: call kernel_param_unlock on error

LU-8066 libcfs: call kernel_param_unlock on error

In libcfs_param_debug_mb_set, kerenl_param_unlock should be
called in case of an error.

Change-Id: Iafeeb21b2d891f4ed7432e4d1ddd3c383fe33d5a
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: https://review.whamcloud.com/28612
Tested-by: Jenkins
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>