sparc: Fix mremap address range validation.

Just like mmap, we need to validate address ranges regardless
of MAP_FIXED.

sparc{,64}_mmap_check()'s flag argument is unused, remove.

Based upon a report and preliminary patch by
Jan Lieskovsky <jlieskov@redhat.com>

Signed-off-by: David S. Miller <davem@davemloft.net>