staging: r8188eu: remove function _rtw_zvmalloc

staging: r8188eu: remove function _rtw_zvmalloc

Remove the function _rtw_zvmalloc from os_dep/osdep_service.c, as this
function is now unused and is just an inline wrapper around vmalloc
which zeroes out the memory. All previous callers have been converted to
use vzalloc. 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/20210818234853.208448-7-phil@philpotter.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>