RDMA/rxe: Remove the unnecessary variable

The variable pkey is assigned from a macro. Then this variable is passed
to a function bth_init directly, and pkey is not used again. So remove it
and use the macro directly.

Fixes: 76251e15 ("RDMA/rxe: Remove pkey table")
Link: https://lore.kernel.org/r/20211207194057.713289-1-yanjun.zhu@linux.dev


Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>