drm/nv50/disp: min/max are reversed in nv50_crtc_gamma_set()

We should be taking the minimum here instead of the max.  It could lead
to a buffer overflow.

Fixes: 438d99e3 ('drm/nvd0/disp: initial crtc object implementation')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

a/drm/nv50_display.c b/drm/nv50_display.c
index f8e66c08b11a..4e384a2f99c3 100644