Add dedicated chip erase function for SST49LF040

Corresponding to flashrom svn r31 and coreboot v2 svn r1852.
diff --git a/flash_rom.c b/flash_rom.c
index 35a9f50..ceb56ad 100644
--- a/flash_rom.c
+++ b/flash_rom.c
@@ -66,7 +66,7 @@
 	{"SST39VF020",	SST_ID,		SST_39VF020,	NULL, 256, 4096,
 	 probe_jedec,	erase_chip_jedec, write_39sf020,NULL},
 	{"SST49LF040",	SST_ID,		SST_49LF040, 	NULL, 512, 4096,
-	 probe_jedec, 	erase_chip_jedec, write_49lf040,NULL},
+	 probe_jedec, 	erase_49lf040, write_49lf040,NULL},
 	{"SST49LF080A",	SST_ID,		SST_49LF080A,	NULL, 1024, 4096,
 	 probe_jedec,	erase_chip_jedec, write_49lf040,NULL},
 	{"SST49LF002A/B", SST_ID,	SST_49LF002A,	NULL, 256, 16 * 1024,