scsi: zfcp: Clean up zfcp_erp_action_ready()

scsi: zfcp: Clean up zfcp_erp_action_ready()

We already maintain a pointer to act->adapter. Use it consistently to avoid
any confusion about whose ->erp_ready_head and ->erp_ready_wq we are
accessing.

Link: https://lore.kernel.org/r/d1bb04322f240dee32f4c4a551bc93bc736f4b01.1593780621.git.bblock@linux.ibm.com
Reviewed-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>