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/chipdrivers.h b/chipdrivers.h
index cb1e877..3c7d146 100644
--- a/chipdrivers.h
+++ b/chipdrivers.h
@@ -62,8 +62,8 @@
 
 
 /* spi25_statusreg.c */
-uint8_t spi_read_status_register(struct flashctx *flash);
-int spi_write_status_register(struct flashctx *flash, int status);
+uint8_t spi_read_status_register(const struct flashctx *flash);
+int spi_write_status_register(const struct flashctx *flash, int status);
 void spi_prettyprint_status_register_bit(uint8_t status, int bit);
 int spi_prettyprint_status_register_plain(struct flashctx *flash);
 int spi_prettyprint_status_register_default_welwip(struct flashctx *flash);