drm/i915/huc: Fix missing error code in intel_huc_init()

Smatch warns:
	drivers/gpu/drm/i915/gt/uc/intel_huc.c:388
	    intel_huc_init() warn: missing error code 'err'

When the allocation of VMAs fail: The value of err is zero at this
point and it is passed to PTR_ERR and also finally returning zero which
is success instead of failure.

Fix this by adding the missing error code when VMA allocation fails.

Fixes: 08872cb1

 ("drm/i915/mtl/huc: auth HuC via GSC")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230614223646.2583633-1-daniele.ceraolospurio@intel.com
(cherry picked from commit ce432fd3

)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>