staging: rtl8188eu: core: Fix coding style issue

Use %s and  __func__ in place of function names.
This solves following checkpatch.pl warning
WARNING: Prefer using '"%s...", __func__' to using 'rtw_do_join', this function's name, in a string

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Link: https://lore.kernel.org/r/20200701145457.9562-1-puranjay12@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>