iwx: Fix 32-bit compilation

• Avoid shifts wider than integer types, by wrapping the corresponding checks into '#if SIZEOF_SIZE_T > 32' blocks. 'bus_addr_t' currently has the same width as 'size_t' on all architectures (and this is not going to change for 32-bit architectures).
• Use appropriate printf(3) format for 'wk_keytsc'.

Reviewed by: adrian
MFC after: 1 minute
MFC to: stable/15
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D55667