lib: sbi: Refine the way to construct platform features

sbi_platform_get_features_str() uses sbi_snprintf() to construct the
features_str. However, it passes the wrong length value (i.e., the nfstr),
which should be (nfstr-offset) as the starting point of str (i.e.,
features_str + offset) changes.

This commit also checks the return value of snprintf, and handles the
corner case that the string buffer is full.

Signed-off-by: Dong Du <Dd_nirvana@sjtu.edu.cn>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

lib/sbi/sbi_platform.c

@@ -48,9 +48,18 @@ void sbi_platform_get_features_str(const struct sbi_platform *plat,
 		if (features & feat) {
 			temp = sbi_platform_feature_id2string(feat);
 			if (temp) {
-				sbi_snprintf(features_str + offset, nfstr,
-					     "%s,", temp);
-				offset = offset + sbi_strlen(temp) + 1;
+				int len = sbi_snprintf(features_str + offset,
+						       nfstr - offset,
+						       "%s,", temp);
+				if (len < 0)
+					break;
+
+				if (offset + len >= nfstr) {
+					/* No more space for features */
+					offset = nfstr;
+					break;
+				} else
+					offset = offset + len;
 			}
 		}
 		feat = feat << 1;