staging: r8188eu: convert only rtw_vmalloc call to vmalloc

staging: r8188eu: convert only rtw_vmalloc call to vmalloc

Convert the only call to rtw_vmalloc in os_dep/ioctl_linux.c to the
kernel's existing vmalloc function, as rtw_malloc is just a preprocessor
definition for _rtw_vmalloc. The _rtw_vmalloc function is defined inline
and returns a u8, wrapping standard vmalloc. This behaviour is not necessary.

Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210818234853.208448-2-phil@philpotter.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>