Fixes gcc '-Wunused-but-set-variable' warning:

drivers/infiniband/hw/bnxt_re/qplib_res.c: In function '__alloc_pbl':
drivers/infiniband/hw/bnxt_re/qplib_res.c:109:13: warning:
 variable 'pg_size' set but not used [-Wunused-but-set-variable]

commit 0c4dcd60 ("RDMA/bnxt_re: Refactor hardware queue memory
allocation") involved this, but not used, so remove it.

Link: https://lore.kernel.org/r/20200227064209.87893-1-yuehaibing@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>