[SCSI] bnx2i: convert bnx2i_dev_lock to mutex

convert bnx2i_dev_lock to type mutex from rwlock_t because
cnic->register_device() can sleep for various reasons including memory
allocation, waiting for ISCSI_INIT completion and while acquiring mutex lock,
cnic_lock.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Anil Veerabhadrappa <anilgv@broadcom.com>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>