swim3: add missing major.h include

swim3 got this through blkdev.h previously, but blkdev.h is not including
it anymore. Include it specifically for the driver, otherwise FLOPPY_MAJOR
is undefined and breaks the compile on PPC if swim3 is configured.

Fixes: b81e0c23 ("block: drop unused includes in <linux/genhd.h>")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/swim3.c

@@ -27,6 +27,7 @@
 #include <linux/module.h>
 #include <linux/spinlock.h>
 #include <linux/wait.h>
+#include <linux/major.h>
 #include <asm/io.h>
 #include <asm/dbdma.h>
 #include <asm/prom.h>