lpfc: Use kzalloc instead of kmalloc

This patch is to the lpfc_els.c which resolves following warning
reported by coccicheck:

WARNING: kzalloc should be used for rdp_context, instead of
kmalloc/memset

Signed-off-by: Punit Vara <punitvara@gmail.com>
Signed-off-by: James Smart <james.smart@avagotech.com>
Reviewed-by: Hannes Reinicke <hare@suse.de>
Reviewed-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Reviewed-by: Sebastian Herbszt <herbszt@gmx.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>