staging: rtl8188eu: make rtw_android_cmdstr_to_num static

This function is used only in rtw_android.c.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210505202622.11087-1-martin@kaiser.cx


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