xprtrdma: Fix MR list handling

xprtrdma: Fix MR list handling

BugLink: https://bugs.launchpad.net/bugs/1861085
commit c3700780a096fc66467c81076ddf7f3f11d639b5 upstream.

Close some holes introduced by commit 6dc6ec9e04c4 ("xprtrdma: Cache
free MRs in each rpcrdma_req") that could result in list corruption.

In addition, the result that is tabulated in @count is no longer
used, so @count is removed.

Fixes: 6dc6ec9e04c4 ("xprtrdma: Cache free MRs in each rpcrdma_req")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>