nfs: count correct array for mnt3_counts array size

Array size of mnt3_counts should be the size of array
mnt3_procedures, not mnt_procedures, though they're same in size
right now. Found this by code inspection.

Fixes: 1c5876dd

 ("sunrpc: move p_count out of struct rpc_procinfo")
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>