jpeg: add jpeg_fetch_size()

This aids the fuzzer test case.

Change-Id: Ic7d43b76cf5660e085e7b3b13499de0358c13197
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/12181
Reviewed-by: Martin Roth <martinroth@google.com>
Tested-by: build bot (Jenkins)

src/lib/jpeg.c

@@ -257,6 +257,18 @@ static int dec_checkmarker(void)
 	return 0;
 }
 
+void jpeg_fetch_size(unsigned char *buf, int *width, int *height)
+{
+	datap = buf;
+	getbyte();
+	getbyte();
+	readtables(M_SOF0);
+	getword();
+	getbyte();
+	*height = getword();
+	*width = getword();
+}
+
 int jpeg_check_size(unsigned char *buf, int width, int height)
 {
   	datap = buf;

src/lib/jpeg.h

@@ -49,6 +49,7 @@ struct jpeg_decdata {
 };
 
 int jpeg_decode(unsigned char *, unsigned char *, int, int, int, struct jpeg_decdata *);
+void jpeg_fetch_size(unsigned char *buf, int *width, int *height);
 int jpeg_check_size(unsigned char *, int, int);
 
 #endif