spi: Pass master instead of flash to .send_command

In the SPI-master API, `.send_command` should only forward commands to
the SPI bus. All details about the commands and the SPI slave should be
handled in the chip driver. Hence, replace the `flashctx` pointer with
one to the `spi_master` to enforce proper separation.

Change-Id: I50934a1294217794b7e23cc98ade7e4279c059a1
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/74897
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/ni845x_spi.c b/ni845x_spi.c
index 177c799..21d39a8 100644
--- a/ni845x_spi.c
+++ b/ni845x_spi.c
@@ -567,7 +567,7 @@
 	return 0;
 }
 
-static int ni845x_spi_transmit(const struct flashctx *flash,
+static int ni845x_spi_transmit(const struct spi_master *mst,
 			       unsigned int write_cnt,
 			       unsigned int read_cnt,
 			       const unsigned char *write_arr,