scsi: be2iscsi: Use kasprintf

Use kasprintf instead of combination of kmalloc and sprintf.  Also,
remove BEISCSI_MSI_NAME macro used to specify size of string as
kasprintf handles size computations.

Signed-off-by: Himanshu Jha <himanshujha199640@gmail.com>
Reviewed-by: Kyle Fortin <kyle.fortin@oracle.com>
Reviewed-by: Jitendra Bhivare <jitendra.bhivare@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>