jit: Add INSN_RESTORE_CALLER_REGS to mark_clobbers()

The mark_clobbers() function doesn't deal with INSN_RESTORE_CALLER_REGS
which causes caller-save register clobbering when calling functions with
the return type void.

Fix that up to make x86-64 behave properly again.

Signed-off-by: Pekka Enberg <penberg@kernel.org>