IB/iser: Simplify prot_caps setting

Reduce the number of instructions made for setting protection caps. No
need to do bitwise OR with 0 since we can zero the return value in the
beginning of the function.

Link: https://lore.kernel.org/r/20210111145754.56727-5-mgurtovoy@nvidia.com


Reviewed-by: Israel Rukshin <israelr@nvidia.com>
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>