ARM: 5740/1: fix valid_phys_addr_range() range check

Commit 1522ac3e
("Fix virtual to physical translation macro corner cases")
breaks the end of memory check in valid_phys_addr_range().
The modified expression results in the apparent /dev/mem size
being 2 bytes smaller than what it actually is.

This patch reworks the expression to correctly check the address,
while maintaining use of a valid address to __pa().

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>