unix: fix calculation of pointers

CID 1141016 (#1 of 1): Extra sizeof expression (SIZEOF_MISMATCH)
suspicious_pointer_arithmetic: Adding "40UL /* sizeof (FilePermsEntry)
*/" to pointer "(FownEntry *)perms" of type "FownEntry *" is suspicious
because adding an integral value to this pointer automatically scales
that value by the size, 48 bytes, of the pointed-to type, "FownEntry".
Most likely, "sizeof (FilePermsEntry)" is extraneous and should be
replaced with 1.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>