drm: use ENOMEM for drmm_kzalloc allocation failures

Other callers of drmm_kzalloc already return -ENOMEM on allocation
failure. Change EINVAL to ENOMEM for consistency.

Signed-off-by: Niels Dossche <dossche.niels@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220521234104.88410-1-dossche.niels@gmail.com