Get rid of open-coding in ia64_brk()

Get rid of open-coding in ia64_brk()

The comment in there used to be true, but these days do_brk() does
the arch-specific check that covers what we open-coded here.  So we
can use sys_brk() just fine, only need to do force_successful_syscall_return()
after it.

See commit fa6a502e0606b0d7754d9675cc938b68828c8ffd - that's when the
checks in do_brk() had been originally added.

Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>