Reinstate lost flush_ioremap_region() fix to pxa2xx-flash driver

Commit 90833fda ("[ARM] 4554/1: replace
consistent_sync() with flush_ioremap_region()") introduced a new
"flush_ioremap_region()" function to be used by the MTD mainstone-flash
and lubbock-flash drivers to fix a regression from around 2.6.18.

Those drivers were independently merged into a single driver by Todd
Poynor in commit e644f7d6 ("[MTD] MAPS:
Merge Lubbock and Mainstone drivers into common PXA2xx driver")

Later, those two commits were merged into the main MTD tree by commit
b160292c ("Merge Linux 2.6.23") by David
Woodhouse, but in that merge, the fix to use flush_iomap_region() got
lost (as it was to files that now no longer existed).

This reinstates the fix in the new driver.

Noticed-by: Russell King <rmk@arm.linux.org.uk>
Tested-and-acked-by: Nicolas Pitre <nico@cam.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Jared Hulbert <jaredeh@gmail.com>
Cc: Todd Poynor <tpoynor@mvista.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>