seq_buf: Avoid type mismatch for seq_buf_init

Building with W=2 prints a number of warnings for one function that
has a pointer type mismatch:

linux/seq_buf.h: In function 'seq_buf_init':
linux/seq_buf.h:35:12: warning: pointer targets in assignment from 'unsigned char *' to 'char *' differ in signedness [-Wpointer-sign]

Change the type in the function prototype according to the type in
the structure.

Link: https://lkml.kernel.org/r/20201026161108.3707783-1-arnd@kernel.org

Fixes: 9a777793 ("tracing: Convert seq_buf fields to be like seq_file fields")
Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/seq_buf.h

@@ -30,7 +30,7 @@ static inline void seq_buf_clear(struct seq_buf *s)
 }
 
 static inline void
-seq_buf_init(struct seq_buf *s, unsigned char *buf, unsigned int size)
+seq_buf_init(struct seq_buf *s, char *buf, unsigned int size)
 {
 	s->buffer = buf;
 	s->size = size;

include/linux/trace_seq.h

@@ -12,7 +12,7 @@
  */
 
 struct trace_seq {
-	unsigned char		buffer[PAGE_SIZE];
+	char			buffer[PAGE_SIZE];
 	struct seq_buf		seq;
 	int			full;
 };
@@ -51,7 +51,7 @@ static inline int trace_seq_used(struct trace_seq *s)
  * that is about to be written to and then return the result
  * of that write.
  */
-static inline unsigned char *
+static inline char *
 trace_seq_buffer_ptr(struct trace_seq *s)
 {
 	return s->buffer + seq_buf_used(&s->seq);