IB/mlx4: Remove unnecessary parentheses

Clang warns when more than one set of parentheses are used in single
conditional statements.

drivers/infiniband/hw/mlx4/mcg.c:676:16: warning: equality comparison
with extraneous parentheses [-Wparentheses-equality]
                        if ((method == IB_MGMT_METHOD_GET_RESP)) {
                             ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/infiniband/hw/mlx4/mcg.c:676:16: note: remove extraneous
parentheses around the comparison to silence this warning
                        if ((method == IB_MGMT_METHOD_GET_RESP)) {
                            ~       ^                         ~
drivers/infiniband/hw/mlx4/mcg.c:676:16: note: use '=' to turn this
equality comparison into an assignment
                        if ((method == IB_MGMT_METHOD_GET_RESP)) {
                                    ^~
                                    =

Remove the unnecessary parentheses to silence this warning.

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>