Revert "serial: set the errno if and only if in thread context"
Revert "serial: set the errno if and only if in thread context"

This reverts commit 07bd09fc0fc256e5c53ad3c6157802fd94c9910c.
The validation of the context is done with in `rt_set_errno`. So it's
safe to call it here.

weiyuliang/rt-thread,nongxiaoming/rt-thread,zhaojuntao/rt-thread,gbcwbz/rt-thread,ArdaFu/rt-thread,weety/rt-thread,yongli3/rt-thread,yongli3/rt-thread,yongli3/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,wolfgangz2013/rt-thread,armink/rt-thread,weety/rt-thread,AubrCool/rt-thread,FlyLu/rt-thread,yongli3/rt-thread,armink/rt-thread,FlyLu/rt-thread,hezlog/rt-thread,AubrCool/rt-thread,AubrCool/rt-thread,weety/rt-thread,weiyuliang/rt-thread,igou/rt-thread,gbcwbz/rt-thread,zhaojuntao/rt-thread,hezlog/rt-thread,hezlog/rt-thread,armink/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,AubrCool/rt-thread,hezlog/rt-thread,wolfgangz2013/rt-thread,wolfgangz2013/rt-thread,AubrCool/rt-thread,gbcwbz/rt-thread,nongxiaoming/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread,FlyLu/rt-thread,ArdaFu/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,weety/rt-thread,weety/rt-thread,weety/rt-thread,wolfgangz2013/rt-thread,hezlog/rt-thread,gbcwbz/rt-thread,armink/rt-thread,FlyLu/rt-thread,yongli3/rt-thread,zhaojuntao/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,ArdaFu/rt-thread,FlyLu/rt-thread,gbcwbz/rt-thread,yongli3/rt-thread,FlyLu/rt-thread,weiyuliang/rt-thread,wolfgangz2013/rt-thread,igou/rt-thread,gbcwbz/rt-thread,zhaojuntao/rt-thread,igou/rt-thread,yongli3/rt-thread,weiyuliang/rt-thread,zhaojuntao/rt-thread,hezlog/rt-thread,RT-Thread/rt-thread,igou/rt-thread,wolfgangz2013/rt-thread,armink/rt-thread,weiyuliang/rt-thread,weiyuliang/rt-thread,RT-Thread/rt-thread,armink/rt-thread,ArdaFu/rt-thread,AubrCool/rt-thread,zhaojuntao/rt-thread,AubrCool/rt-thread,zhaojuntao/rt-thread,hezlog/rt-thread,ArdaFu/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,weiyuliang/rt-thread,igou/rt-thread,ArdaFu/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,ArdaFu/rt-thread,igou/rt-thread,wolfgangz2013/rt-thread,igou/rt-thread,FlyLu/rt-thread,armink/rt-thread,weety/rt-thread,gbcwbz/rt-thread