mm: simplify min_brk handling in brk()

mm: simplify min_brk handling in brk()

Set min_brk to mm->start_brk by default, and override it with mm->end_data
only when CONFIG_COMPAT_BRK is enabled and brk_randomized is false.

This makes the logic clearer with no functional change.

Link: https://lkml.kernel.org/r/20250710025859.926355-1-liuqiye2025@163.com
Signed-off-by: Xuanye Liu <liuqiye2025@163.com>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>