meta: Don't alter fragment color clamp in DrawPixels().

meta: Don't alter fragment color clamp in DrawPixels().

DrawPixels uses the MESA_META_CLAMP_FRAGMENT_COLOR flag to save/restore
the fragment color clamp mode.  This is unnecessary since it never
alters it.  It's also harmful: when the clamp mode is GL_FIXED_ONLY,
setting this flag causes _mesa_meta_begin to force it to GL_FALSE,
breaking clamping on SNORM formats.

DrawPixels should use the user-specified clamp mode and not change it.

Fixes Piglit's spec/ARB_color_buffer_float/GL_RGBA8_SNORM-drawpixels
test on i965/Sandybridge (with SNORM render targets re-enabled).

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>