gsm0503_tch_hr_decode(): look at all 8 stealing bits

This function needs to look at hl and hu stealing bits in order to
decide if it should decode FACCH/H instead of TCH/HS traffic.
However, out of the 8 (in total) hl and hu bits that get set when
FACCH/H stealing takes place, the function only looked at 7 of them
- one was missed.  Fix this bug.

Change-Id: I08c4358b26d69910190f89a53b654bc58c2efea9
diff --git a/src/coding/gsm0503_coding.c b/src/coding/gsm0503_coding.c
index 3fd440f..ce24650 100644
--- a/src/coding/gsm0503_coding.c
+++ b/src/coding/gsm0503_coding.c
@@ -1997,7 +1997,7 @@
 			steal -= h;
 		}
 
-		for (i = 2; i < 5; i++) {
+		for (i = 2; i < 6; i++) {
 			gsm0503_tch_burst_unmap(NULL, &bursts[i * 116], &h, 1);
 			steal -= h;
 		}