panfrost: decode: Fix decode_bifrost_constant() prototype

We expect a float, not an integer.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6886>
diff --git a/src/panfrost/lib/decode.c b/src/panfrost/lib/decode.c
index 6356796..ef0d151 100644
--- a/src/panfrost/lib/decode.c
+++ b/src/panfrost/lib/decode.c
@@ -589,7 +589,7 @@
 
 /* Decodes a Bifrost blend constant. See the notes in bifrost_blend_rt */
 
-static unsigned
+static float
 decode_bifrost_constant(u16 constant)
 {
         float lo = (float) (constant & 0xFF);