cuda: fix len calculation in cuda_adb_req

When advancing buffer by 1, len should be shorthened by appropriate
amount, instead of setting it to -1.

Found with cppcheck.

Signed-off-by: Amadeusz Sławiński <amade@asmblr.net>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>

drivers/cuda.c

diff --git a/drivers/cuda.c b/drivers/cuda.c
index 86d2ddb..93a935a 100644
--- a/drivers/cuda.c
+++ b/drivers/cuda.c
@@ -162,7 +162,7 @@
         }
     } else {
         pos = buffer + 1;
-        len = -1;
+        len -= 1;
     }
     memcpy(rcv_buf, pos, len);