firewire: ohci: optimize find_branch_descriptor()

When z==2, the condition "key == 2" is superfluous because it cannot
occur without "b == 3", as a descriptor with b!=3 and key==2 would be
an OUTPUT_MORE_IMMEDIATE descriptor which cannot be used alone.

Also remove magic numbers and needless computations on the b field.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/ohci.c

@@ -1006,13 +1006,12 @@ static void ar_context_run(struct ar_context *ctx)
 
 static struct descriptor *find_branch_descriptor(struct descriptor *d, int z)
 {
-	int b, key;
+	__le16 branch;
 
-	b   = (le16_to_cpu(d->control) & DESCRIPTOR_BRANCH_ALWAYS) >> 2;
-	key = (le16_to_cpu(d->control) & DESCRIPTOR_KEY_IMMEDIATE) >> 8;
+	branch = d->control & cpu_to_le16(DESCRIPTOR_BRANCH_ALWAYS);
 
 	/* figure out which descriptor the branch address goes in */
-	if (z == 2 && (b == 3 || key == 2))
+	if (z == 2 && branch == cpu_to_le16(DESCRIPTOR_BRANCH_ALWAYS))
 		return d;
 	else
 		return d + z - 1;