i965: Set SWIZZLE_NOOP for unused texture units in the program keys.

i965: Set SWIZZLE_NOOP for unused texture units in the program keys.

Previously, we left the swizzle key field as zero for unused texture
units.  The precompile sets all of them to SWIZZLE_NOOP, which meant
that we mismatched almost every time.

Since either works equally well, change it to SWIZZLE_NOOP to match
the precompiles.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>