drm: Use vsnprintf extension %ph

Using the extension saves a bit of code.

Miscellanea:

o Neaten and simplify dump_dp_payload_table
o Removed trailing blank space from output

$ size drivers/gpu/drm/drm_dp_mst_topology.o.* drivers/gpu/drm/tinydrm/*.o*
   text	   data	    bss	    dec	    hex	filename
  25848	      0	     16	  25864	   6508	drivers/gpu/drm/drm_dp_mst_topology.o.new
  26091	      0	     16	  26107	   65fb	drivers/gpu/drm/drm_dp_mst_topology.o.old
   3362	      2	      0	   3364	    d24	drivers/gpu/drm/tinydrm/mipi-dbi.o.new
   3376	      2	      0	   3378	    d32	drivers/gpu/drm/tinydrm/mipi-dbi.o.old

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/a78a21b5f34947da65473a0b7326922cda51a3be.1496187315.git.joe@perches.com
diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c b/drivers/gpu/drm/tinydrm/mipi-dbi.c
index f4eb412..c83eeb7 100644
--- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
+++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
@@ -914,7 +914,7 @@ static int mipi_dbi_debugfs_command_show(struct seq_file *m, void *unused)
 {
 	struct mipi_dbi *mipi = m->private;
 	u8 cmd, val[4];
-	size_t len, i;
+	size_t len;
 	int ret;
 
 	for (cmd = 0; cmd < 255; cmd++) {
@@ -943,10 +943,7 @@ static int mipi_dbi_debugfs_command_show(struct seq_file *m, void *unused)
 			seq_puts(m, "XX\n");
 			continue;
 		}
-
-		for (i = 0; i < len; i++)
-			seq_printf(m, "%02x", val[i]);
-		seq_puts(m, "\n");
+		seq_printf(m, "%*phN\n", (int)len, val);
 	}
 
 	return 0;