[ARM] 3292/1: Fix memory corruption in asm-arm/checksum.h: ip_fast_csum()

Patch from Richard Purdie

ip_fast_csum() accesses memory via a pointer (iph) within an
asm function. To prevent memory corruption when the function is
inlined, it needs "memory" on the clobber list.

This fixes ip checksum errors reported by a Zaurus user.

Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>