Die on failed /incbin/ seeks

Failing to open an input file, with /include/ or /incbin/ is treated as
immediately fatal inside srcfile_relative_open().  However, filing to
seek() to the requested offset in an /incbin/ is not.  This is a bit oddly
inconsistent, and leaves us with a strange case that's awkward to deal with
down the line.

So, get rid of it and have failed seeks on an /incbin/ be immediately
fatal.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/dtc-parser.y b/dtc-parser.y
index efe81dd..bed857e 100644
--- a/dtc-parser.y
+++ b/dtc-parser.y
@@ -226,10 +226,9 @@
 
 			if ($6 != 0)
 				if (fseek(f, $6, SEEK_SET) != 0)
-					print_error("Couldn't seek to offset %llu in \"%s\": %s",
-						     (unsigned long long)$6,
-						     $4.val,
-						     strerror(errno));
+					die("Couldn't seek to offset %llu in \"%s\": %s",
+					    (unsigned long long)$6, $4.val,
+					    strerror(errno));
 
 			d = data_copy_file(f, $8);