ARM: l2c: fix revision checking

The revision checking in l2c310_enable() was not correct; we were
masking the part number rather than the revision number.  Fix this
to use the correct macro.

Fixes: 4374d649 ("ARM: l2c: add automatic enable of early BRESP")
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>