Use a distinct return code for SPI commands with unsupported/invalid length

Some drivers support only a few combinations of read/write length and
return error otherwise. Having a distinct return code for this error
means we can handle it in upper layers.

Corresponding to flashrom svn r653.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Stefan Reinauer <stepan@coresystems.de>
diff --git a/it87spi.c b/it87spi.c
index d5f7a51..41ce6db 100644
--- a/it87spi.c
+++ b/it87spi.c
@@ -170,7 +170,7 @@
 	if (readcnt > 3) {
 		printf("%s called with unsupported readcnt %i.\n",
 		       __FUNCTION__, readcnt);
-		return 1;
+		return SPI_INVALID_LENGTH;
 	}
 	switch (writecnt) {
 	case 1:
@@ -200,7 +200,7 @@
 	default:
 		printf("%s called with unsupported writecnt %i.\n",
 		       __FUNCTION__, writecnt);
-		return 1;
+		return SPI_INVALID_LENGTH;
 	}
 	/*
 	 * Start IO, 33 or 16 MHz, readcnt input bytes, writecnt output bytes.