scsi: megaraid: Remove set but unused variable

In mega_build_cmd(), the variable epthru is set but not used. Remove it to
avoid a compiler warning.

Link: https://lore.kernel.org/r/20200706123349.451915-1-damien.lemoal@wdc.com


Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>