s390/mm: mmap base does not depend on ADDR_NO_RANDOMIZE personality

randomize_stack_top() checks for current task flag PF_RANDOMIZE in order
to use stack randomization and PF_RANDOMIZE is set when
ADDR_NO_RANDOMIZE is unset, so no need to check for ADDR_NO_RANDOMIZE
in stack_maxrandom_size.

[heiko.carstens@de.ibm.com]: See also commit 01578e36 ("x86/elf:
Remove the unnecessary ADDR_NO_RANDOMIZE checks")

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>