crypto: arm64/sha256 - fix build when CONFIG_PREEMPT_VOLUNTARY=y

Fix the build of sha256-ce.S when CONFIG_PREEMPT_VOLUNTARY=y by passing
the correct label to the cond_yield macro. Also adjust the code to
execute only one branch instruction when CONFIG_PREEMPT_VOLUNTARY=n.

Fixes: 6e36be511d28 ("crypto: arm64/sha256 - implement library instead of shash")
Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Signed-off-by: Eric Biggers <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

arch/arm64/lib/crypto/sha256-ce.S

···
 	add		dgav.4s, dgav.4s, dg0v.4s
 	add		dgbv.4s, dgbv.4s, dg1v.4s
 
+	/* return early if voluntary preemption is needed */
+	cond_yield	1f, x5, x6
+
 	/* handled all input blocks? */
-	cbz		x2, 1f
-	cond_yield	3f, x5, x6
-	b		0b
+	cbnz		x2, 0b
 
 	/* store new state */
 1:	st1		{dgav.4s, dgbv.4s}, [x0]