Fix a few incorrectly checked [io_]remap_pfn_range() calls

commit 7314e613d5ff9f0934f7a0f74ed7973b903315d1 upstream.

Nico Golde reports a few straggling uses of [io_]remap_pfn_range() that
really should use the vm_iomap_memory() helper.  This trivially converts
two of them to the helper, and comments about why the third one really
needs to continue to use remap_pfn_range(), and adds the missing size
check.

Reported-by: Nico Golde <nico@ngolde.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org.
[bwh: Backported to 3.2:
 - Adjust context
 - Also remove redundant vm_flags changes, removed separately upstream]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>