scsi: mptsas: remove duplicated assignment to pointer head

The pointer head is re-assigned the same value twice, so remove the
second redundant assignment.

Cleans up clang warning:
drivers/message/fusion/mptsas.c:1161:20: warning: Value stored to 'head'
during its initialization is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>