parasite: pass parameter regs as pointer

CID 163751 (#1 of 1): Big parameter passed by value (PASS_BY_VALUE)
pass_by_value: Passing parameter regs of type user_regs_struct_t (size 224 bytes) by value.

Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>