LU-12370 ptlrpc: grammar fix.

LU-12370 ptlrpc: grammar fix.

ptlrpc_invalidate_import() error message grammar fix.

Test-Parameters: trivial
Cray-bug-id: LUS-4015
Change-Id: Ic1a99440f381ed982e348267996e4523aef8ebad
Signed-off-by: Alexander Zarochentsev <c17826@cray.com>
Reviewed-on: https://review.whamcloud.com/36508
Reviewed-by: Andrew Perepechko <c17827@cray.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Stephan Thiell <sthiell@stanford.edu>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.super@gmail.com>
Reviewed-by: Colin Faber <cfaber@cray.com>