isdn/hisax: Remove unnecessary parenthesis

Clang warns when more than one set of parentheses are used for single
conditional statements:

drivers/isdn/hisax/w6692.c:627:30: warning: equality comparison with
extraneous parentheses [-Wparentheses-equality]
                if ((cs->dc.w6692.ph_state == W_L1IND_DRD)) {
                     ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
drivers/isdn/hisax/w6692.c:627:30: note: remove extraneous parentheses
around the comparison to silence this warning
                if ((cs->dc.w6692.ph_state == W_L1IND_DRD)) {
                    ~                      ^             ~
drivers/isdn/hisax/w6692.c:627:30: note: use '=' to turn this equality
comparison into an assignment
                if ((cs->dc.w6692.ph_state == W_L1IND_DRD)) {
                                           ^~
                                           =
1 warning generated.

Remove the parentheses to silence this warning.

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>