V4L/DVB (13285): vpfe_capture: keep index within bound in vpfe_cropcap()

If vpfe_dev->std_index equals ARRAY_SIZE(vpfe_standards), that is
one too large.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Muralidharan Karicheri <m-karicheri2@ti.com>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>