tty: tty_buffer: switch data type to u8

There is no reason to have tty_buffer::data typed as unsigned long.
Switch to u8, but preserve the ulong alignment using __aligned.

This allows for the cast removal from char_buf_ptr(). And for use of
struct_size() in the allocation in tty_buffer_alloc() -- in the next
patch.

Signed-off-by: "Jiri Slaby (SUSE)" <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/linux/tty_buffer.h

···
 	unsigned int read;
 	bool flags;
 	/* Data points here */
-	unsigned long data[];
+	u8 data[] __aligned(sizeof(unsigned long));
 };
 
 static inline u8 *char_buf_ptr(struct tty_buffer *b, unsigned int ofs)
 {
-	return ((u8 *)b->data) + ofs;
+	return b->data + ofs;
 }
 
 static inline u8 *flag_buf_ptr(struct tty_buffer *b, unsigned int ofs)