Let the flash context directly point to the used master

We used to have a pointer to a full `registered_master` struct in
our flash context. Beside the used master, this contained a bit
mask of supported buses. Oddly convenient, this bit mask invited
to bypass the chip driver and break the abstraction. It allowed
to place bus-specific details virtually anywhere in flashprog,
making it harder to find a good place for them.

So, get rid of the `buses_supported` bit mask by pointing directly
to the master. Only the chip driver will implicitly know which type
of master is used.

Change-Id: I9ce13d8df0e7ccc67519d888dd9cb2e2ff8d6682
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/72533
diff --git a/ft2232_spi.c b/ft2232_spi.c
index e3b19d0..889db98 100644
--- a/ft2232_spi.c
+++ b/ft2232_spi.c
@@ -215,7 +215,7 @@
 /* Returns 0 upon success, a negative number upon errors. */
 static int ft2232_spi_send_multicommand(const struct flashctx *flash, struct spi_command *cmds)
 {
-	struct ft2232_data *spi_data = flash->mst->spi.data;
+	struct ft2232_data *spi_data = flash->mst.spi->data;
 	struct ftdi_context *ftdic = &spi_data->ftdi_context;
 	static unsigned char buf[FTDI_HW_BUFFER_SIZE];
 	size_t i = 0;