patch 9.1.0540: Unused assignment in sign_define_cmd()

Problem:  Unused assignment in sign_define_cmd()
Solution: Remove the assignment.  Also document the "priority" flag of
          sign_define(). (zeertzjq)

closes: #15169

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/sign.txt b/runtime/doc/sign.txt
index 84b2977..679099c 100644
--- a/runtime/doc/sign.txt
+++ b/runtime/doc/sign.txt
@@ -1,4 +1,4 @@
-*sign.txt*      For Vim version 9.1.  Last change: 2024 Jul 06
+*sign.txt*      For Vim version 9.1.  Last change: 2024 Jul 07
 
 
 		  VIM REFERENCE MANUAL    by Gordon Prieur
@@ -404,6 +404,7 @@
 		   icon		full path to the bitmap file for the sign.
 		   linehl	highlight group used for the whole line the
 				sign is placed in.
+		   priority	default priority value of the sign
 		   numhl	highlight group used for the line number where
 				the sign is placed.
 		   text		text that is displayed when there is no icon
diff --git a/src/sign.c b/src/sign.c
index 1ae714d..b1f496c 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -1390,7 +1390,6 @@
 	{
 	    arg += 9;
 	    prio = atoi((char *)arg);
-	    arg = skiptowhite(arg);
 	}
 	else
 	{
diff --git a/src/version.c b/src/version.c
index 456f2d6..da584b9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    540,
+/**/
     539,
 /**/
     538,