staging: r8188eu: remove function _rtw_vmalloc

staging: r8188eu: remove function _rtw_vmalloc

Remove the function _rtw_vmalloc from os_dep/osdep_service.c, converting
its only user (also in os_dep/osdep_service.c) to use plain vmalloc.
This function is just an inline wrapper around vmalloc which returns a u8
pointer, which isn't needed. Also remove the declaration from
include/osdep_service.h.

It is considered generally bad practice to declare functions as inline in
the majority of cases, as not only can this qualifier be ignored by the
compiler but the compiler generally makes good decisions about inlining
anyway.

Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210818234853.208448-4-phil@philpotter.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>