IB/mthca: Use non-atomic bitmap functions when possible in 'mthca_allocator.c'

The accesses to the 'alloc->table' bitmap are protected by the
'alloc->lock' spinlock, so no concurrent accesses can happen.

So prefer the non-atomic '__[set|clear]_bit()' functions to save a few
cycles.

Link: https://lore.kernel.org/r/5f909ca1284fa4d2cf13952b08b9e303b656c968.1637785902.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>