staging: r8188eu: os_dep: Hoist vmalloc.h include into osdep_service.h

After commit 71f09c5ae9 ("staging: r8188eu: Remove wrapper around
vfree"), the driver fails to build on Hexagon due to an implicit
declaration in several different files:

drivers/staging/r8188eu/core/rtw_mlme.c:129:3: error: implicit
declaration of function 'vfree'
[-Werror,-Wimplicit-function-declaration]
                vfree(pmlmepriv->free_bss_buf);
                ^
1 error generated.

Previously, vfree() was only called in osdep_service.c, which includes
vmalloc.h for vmalloc() and vfree(). Now, the driver relies on vfree()
getting implicitly included from another file.

Hoist the vmalloc.h include from osdep_service.c to osdep_service.h so
that the driver continues to build fine on all architectures.

Fixes: 71f09c5ae9 ("staging: r8188eu: Remove wrapper around vfree")
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20210811005505.3953122-1-nathan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/r8188eu/include/osdep_service.h

@@ -39,6 +39,7 @@
 #include <linux/interrupt.h>	/*  for struct tasklet_struct */
 #include <linux/ip.h>
 #include <linux/kthread.h>
+#include <linux/vmalloc.h>
 
 #include <linux/usb.h>
 #include <linux/usb/ch9.h>

drivers/staging/r8188eu/os_dep/osdep_service.c

@@ -6,7 +6,6 @@
 #include "../include/osdep_service.h"
 #include "../include/drv_types.h"
 #include "../include/recv_osdep.h"
-#include "../include/linux/vmalloc.h"
 #include "../include/rtw_ioctl_set.h"
 
 /*