scsi: mpt3sas: Remove unnecessary parentheses and simplify null checks

Clang warns when multiple pairs of parentheses are used for a single
conditional statement.

drivers/scsi/mpt3sas/mpt3sas_base.c:535:11: warning: equality comparison
with extraneous parentheses [-Wparentheses-equality]
        if ((ioc == NULL))
             ~~~~^~~~~~~
drivers/scsi/mpt3sas/mpt3sas_base.c:535:11: note: remove extraneous
parentheses around the comparison to silence this warning
        if ((ioc == NULL))
            ~    ^      ~
drivers/scsi/mpt3sas/mpt3sas_base.c:535:11: note: use '=' to turn this
equality comparison into an assignment
        if ((ioc == NULL))
                 ^~
                 =
drivers/scsi/mpt3sas/mpt3sas_base.c:539:12: warning: equality comparison
with extraneous parentheses [-Wparentheses-equality]
        if ((pdev == NULL))
             ~~~~~^~~~~~~
drivers/scsi/mpt3sas/mpt3sas_base.c:539:12: note: remove extraneous
parentheses around the comparison to silence this warning
        if ((pdev == NULL))
            ~     ^      ~
drivers/scsi/mpt3sas/mpt3sas_base.c:539:12: note: use '=' to turn this
equality comparison into an assignment
        if ((pdev == NULL))
                  ^~
                  =
2 warnings generated.

Remove them and while we're at it, simplify the NULL checks as '!var' is
used more than 'var == NULL'.

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>