Fix access_ok macro no to permit
case where user will try to access
the last address space which is equal
to segment address.

Example:
segment addr = 0xbfff ffff
address = 0xbfff fff0
size = 0x10

Current wrong implementation
0xbfff ffff >= (0xbfff fff0 | 0x10 | (0xbfff fff0 + 0x10))
0xbfff ffff >= (0xbfff fff0        | 0xc000 0000)
0xbfff ffff >= 0xf000 0000
return 0 which is access failed even the combination is valid.
because get_fs().seq returns the last valid address.

This patch fix this problem.

Size equals to zero is valid access.
Signed-off-by: Michal Simek <michal.simek@xilinx.com>