lib/halfmd4.c: use rol32 inline function in the ROUND macro

<linux/bitops.h> provides rol32() inline function, let's use already
predefined function instead of direct expression.

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Cc: 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>