rwsem: fix commas in initialisation

Leading comma prevents arbitrary reordering of initialisation clauses.
The whole point of C99 initialisation is to allow any such reordering.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200711145954.GA1178171@localhost.localdomain