kcfpool_alloc() should have its argument list marked void

This error occurred when building on Gentoo with debugging enabled:

zfs-kmod-2.1.6/work/zfs-2.1.6/module/icp/core/kcf_sched.c:1277:14:
error: a function declaration without a prototype is deprecated
in all versions of C [-Werror,-Wstrict-prototypes]

kcfpool_alloc()
             ^
             void

1 error generated.

This function is not present in master.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #14023