freedreno/a2xx: Fix compiler warning in disasm.

freedreno/a2xx: Fix compiler warning in disasm.

warning: converting a packed ‘instr_cf_t’ {aka ‘union <anonymous>’}
pointer (alignment 1) to a ‘uint16_t’ {aka ‘short unsigned int’} pointer
(alignment 2) may result in an unaligned pointer value
[-Waddress-of-packed-member]

We may know that we'll only ever have aligned instr_cf_ts, but gcc
doesn't.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5955>