ARM: remove unnecessary cache flush

This cache flush occurs when we first insert a page into the page
tables, where a page did not exist previously.  There can be no
cache lines associated with this virtual mapping, so this cache
flush is redundant.

Tested-by: Mike Rapoport <mike@compulab.co.il>
Tested-by: Mikael Pettersson <mikpe at it.uu.se>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>