scsi: message: fusion: Remove redundant variable dmp

Variable dmp is being assigned a value that is never read, the variable is
redundant and can be removed.

Cleans up clang scan build warning:
drivers/message/fusion/mptbase.c:6667:39: warning: Although
the value stored to 'dmp' is used in the enclosing expression,
the value is never actually read from 'dmp' [deadcode.DeadStores]

Link: https://lore.kernel.org/r/20220318003927.81471-1-colin.i.king@gmail.com
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>