Only try to check erase opcodes for SPI25 chips

Calling spi_get_opcode_from_erasefn() is only valid when
the SPI25 command set is advertised. Note, this includes
AT45 chips that are partially compatible.

Change-Id: I1800e9a4bc1079a37758722e1924a13cd3e7a4c5
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/246
diff --git a/flashprog.c b/flashprog.c
index 30e5668..8102f21 100644
--- a/flashprog.c
+++ b/flashprog.c
@@ -828,7 +828,7 @@
 		return 1;
 	}
 
-	if (flash->chip->bustype == BUS_SPI) {
+	if (flash->chip->bustype == BUS_SPI && flash->chip->spi_cmd_set == SPI25) {
 		bool native_4ba;
 		int i;