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/include/programmer.h b/include/programmer.h
index 418eadd..edef52b 100644
--- a/include/programmer.h
+++ b/include/programmer.h
@@ -498,11 +498,11 @@
 /* spi_master feature checks */
 static inline bool spi_master_4ba(const struct flashctx *const flash)
 {
-	return flash->mst->spi.features & SPI_MASTER_4BA;
+	return flash->mst.spi->features & SPI_MASTER_4BA;
 }
 static inline bool spi_master_no_4ba_modes(const struct flashctx *const flash)
 {
-	return flash->mst->spi.features & SPI_MASTER_NO_4BA_MODES;
+	return flash->mst.spi->features & SPI_MASTER_NO_4BA_MODES;
 }
 
 /* usbdev.c */