target/breakpoints: make breakpoint_watchpoint_remove_all static

Fixes below Sparse tool warning.
warning: symbol 'breakpoint_watchpoint_remove_all' was not declared.
Should it be static?

Signed-off-by: Erhan Kurubas <erhan.kurubas@espressif.com>
Change-Id: I4af1d5aa54abcb45f746b877513ba0b5fccbeb47
Reviewed-on: https://review.openocd.org/c/openocd/+/7955
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins
Reviewed-by: Jan Matyas <jan.matyas@codasip.com>
Reviewed-by: Marek Vrbka <marek.vrbka@codasip.com>

src/target/breakpoints.c

@@ -425,7 +425,7 @@ static int watchpoint_remove_all_internal(struct target *target)
 	return retval;
 }
 
-int breakpoint_watchpoint_remove_all(struct target *target, enum breakpoint_watchpoint bp_wp)
+static int breakpoint_watchpoint_remove_all(struct target *target, enum breakpoint_watchpoint bp_wp)
 {
 	assert(bp_wp == BREAKPOINT || bp_wp == WATCHPOINT);
 	int retval = ERROR_OK;