Fix kern.evdev.rcpt_mask on powerpc

In r360126, I meant to have a different mask only on powerpc, not powerpc64.
Update the check to check that we're not compiling for powerpc64.

Reported by: jhibbits
Approved by: wulf (implicit)
MFC after: 2 weeks
X-MFC-Note: 12 only
X-MFC-With: r360126
Differential Revision: D24370 (followup)