net: hsr/prp: fix cppcheck 'warning: Clarify calculation precedence'

kernel test robot reported following warning:-

In file included from net/hsr/hsr_device.c:
net/hsr/hsr_device.c:465:21: warning: Clarify calculation precedence for '&' and '?'. [clarifyCalculation]
           IFF_ALLMULTI ? 1 : -1);
                        ^
This patch fixes the issue by adding parenthesis around the expression.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>