sparc: increase NR_syscalls properly

sparc: increase NR_syscalls properly

When waitfd() was added, NR_syscalls was never incremented, so
the syscall always unconditionally returned -ENOSYS on SPARC.
Wire it up by incrementing NR_syscalls correctly.

(The syscall has been tested, but, it turns out, only on x86 and
on SPARC in the 4.0 kernel.  Testing on SPARC with its single
user, DTrace, suggests that all is still well here.)

Orabug: 22390316
Reviewed-by: Todd Vierling <todd.vierling@oracle.com>
Signed-off-by: Nick Alcock <nick.alcock@oracle.com>