LU-4586 ptlrpc: cast type in the swith op

LU-4586 ptlrpc: cast type in the swith op

should allow to build with gcc-4.7.2

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: I489ea927d3dc87a7b01f57c5d390612c015b8c47
Reviewed-on: http://review.whamcloud.com/9130
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Li Xi <pkuelelixi@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>