lib/decompress: set the compressor name to NULL on error

Without this we end up using the previous name of the compressor in the
loop in unpack_rootfs.  For example we get errors like "compression
method gzip not configured" even when we have CONFIG_DECOMPRESS_GZIP
enabled.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/decompress.c b/lib/decompress.c
index 528ff93..62696df 100644
--- a/lib/decompress.c
+++ b/lib/decompress.c
@@ -59,8 +59,11 @@
 {
 	const struct compress_format *cf;
 
-	if (len < 2)
+	if (len < 2) {
+		if (name)
+			*name = NULL;
 		return NULL;	/* Need at least this much... */
+	}
 
 	pr_debug("Compressed data magic: %#.2x %#.2x\n", inbuf[0], inbuf[1]);