tree/: Make probe_opcode() flashctx argument const

Probing an opcode generally shouldn't involve mutating the flashctx
state and currently no probe_opcode functions do that.

Make the flashctx arg const so that call sites don't need to have a
non-const pointer.

Tested: ninja test

Change-Id: I19e98be50d682de2d2715417f8b7b8c62b871617
Signed-off-by: Nikolai Artemiev <nartemiev@google.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/70030
Original-Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Original-Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72543
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/ichspi.c b/ichspi.c
index ee29288..afedaf2 100644
--- a/ichspi.c
+++ b/ichspi.c
@@ -1572,7 +1572,7 @@
 	return ret;
 }
 
-static bool ich_spi_probe_opcode(struct flashctx *flash, uint8_t opcode)
+static bool ich_spi_probe_opcode(const struct flashctx *flash, uint8_t opcode)
 {
 	return find_opcode(curopcodes, opcode) >= 0;
 }