const'ify flashctx to align signatures with cros flashrom

The ChromiumOS flashrom fork has since const'ify flashctx
in a few places. This aligns the function signatures to
match with downstream to ease forward porting patches
out of downstream back into mainline flashrom.

This patch is minimum viable alignment and so feedback is
welcome.

Change-Id: Iff6dbda13cb0d941481c0d204b9c30895630fbd1
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/40324
Original-Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/70933
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/dummyflasher.c b/dummyflasher.c
index b9f6126..e1a1d80 100644
--- a/dummyflasher.c
+++ b/dummyflasher.c
@@ -93,7 +93,7 @@
 
 static unsigned int spi_write_256_chunksize = 256;
 
-static int dummy_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int dummy_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 				  const unsigned char *writearr, unsigned char *readarr);
 static int dummy_spi_write_256(struct flashctx *flash, const uint8_t *buf,
 			       unsigned int start, unsigned int len);
@@ -818,7 +818,7 @@
 }
 #endif
 
-static int dummy_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+static int dummy_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 				  unsigned int readcnt,
 				  const unsigned char *writearr,
 				  unsigned char *readarr)