accel/ivpu: avoid duplicate assignment

With extra warnings enabled, gcc warns about two assignments
of the same .mmap callback:

In file included from drivers/accel/ivpu/ivpu_drv.c:10:
include/drm/drm_accel.h:31:27: error: initialized field overwritten [-Werror=override-init]
   31 |         .mmap           = drm_gem_mmap
      |                           ^~~~~~~~~~~~
drivers/accel/ivpu/ivpu_drv.c:360:9: note: in expansion of macro 'DRM_ACCEL_FOPS'
  360 |         DRM_ACCEL_FOPS,
      |         ^~~~~~~~~~~~~~

Remove the unused local assignment.

Fixes: e868cc59 ("accel: Add .mmap to DRM_ACCEL_FOPS")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230126163804.3648051-2-arnd@kernel.org