Avoid divide in IS_ALIGN

I was happy to discover the brand new IS_ALIGN macro and quickly used it in
my code.  To my dismay I found that the generated code used division to
perform the test.

This patch fixes it by changing the % test to an &.  This avoids the
division.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>