staging: rtl8723bs: remove thread wraper functions and add IS_ERR() check

staging: rtl8723bs: remove thread wraper functions and add IS_ERR() check

The rtl8723b_start_thread() and rtl8723b_stop_thread() functions are
wrappers that are only called from one place each. Remove these wrapper
functions and inline the thread handling directly in
rtw_start_drv_threads() and rtw_stop_drv_threads().

This also fixes a bug where kthread_run() was not checked for errors
using IS_ERR(). kthread_run() returns ERR_PTR(-ENOMEM) on failure, not
NULL. Without this check, the SdioXmitThread pointer could contain an
error value, causing issues when rtw_stop_drv_threads() later attempts
to use it.

The inlined code now follows the same pattern as xmitThread and
cmdThread in rtw_start_drv_threads(), with proper IS_ERR() checking.

Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@oracle.com>
Link: https://patch.msgid.link/20260130001641.17941-4-samasth.norway.ananda@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>