rv: Remove redundant assignment to variable retval

Variable retval is being assigned a value that is never read, it is
being re-assigned a new value in both paths of a following if statement.
Remove the assignment.

Cleans up clang-scan warning:
kernel/trace/rv/rv.c:293:2: warning: Value stored to 'retval' is never read [deadcode.DeadStores]
        retval = count;

Link: https://lkml.kernel.org/r/20230418150018.3123753-1-colin.i.king@gmail.com

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: ColinIanKing

kernel/trace/rv/rv.c

@@ -290,8 +290,6 @@ static ssize_t monitor_enable_write_data(struct file *filp, const char __user *u
 	if (retval)
 		return retval;
 
-	retval = count;
-
 	mutex_lock(&rv_interface_lock);
 
 	if (val)