staging: rtl8723bs: Change type of variables and return type

Change type of local variables 'res' and return type of functions
'rtw_init_cmd_pri' and 'rtw_init_evt_priv', as function's
return types are defined for standard error codes _SUCCESS and _FAIL.
Also, change return type of functions declarations corresponding to
change made in function definitions.

Signed-off-by: Madhumitha Prabakaran <madhumithabiw@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>