gsm0411_utils.c: Fix compilation warnings

gsm0411_utils.c:102:2: warning: #warning find a portable way to obtain timezone offset [-Wcpp]
 #warning find a portable way to obtain timezone offset

gsm0411_utils.c: In function 'gsm338_get_sms_alphabet':
gsm0411_utils.c:260:4: warning: large integer implicitly truncated to unsigned type [-Woverflow]
    return 0xffffffff;

Change-Id: I1d6cb31f38721f79e2cf93f9b8e4776f3720aa07
diff --git a/src/gsm/gsm0411_utils.c b/src/gsm/gsm0411_utils.c
index 7c7164c..1d3ef49 100644
--- a/src/gsm/gsm0411_utils.c
+++ b/src/gsm/gsm0411_utils.c
@@ -100,7 +100,7 @@
 #ifdef HAVE_TM_GMTOFF_IN_TM
 	*scts++ = gsm411_bcdify(tm->tm_gmtoff/(60*15));
 #else
-#warning find a portable way to obtain timezone offset
+#pragma message ("find a portable way to obtain timezone offset")
 	*scts++ = 0;
 #endif
 }
@@ -258,7 +258,7 @@
 		if (cgbits & 2) {
 			LOGP(DLSMS, LOGL_NOTICE,
 			     "Compressed SMS not supported yet\n");
-			return 0xffffffff;
+			return -1;
 		}
 
 		switch ((dcs >> 2)&0x03) {