drm/imagination: annotate pvr_fw_version_packed() with __maybe_unused

Building with clang and W=1 leads to warning about unused
pvr_fw_version_packed(). Fix by annotating it with __maybe_unused.

See also commit 6863f5643d ("kbuild: allow Clang to find unused static
inline functions for W=1 build").

Reviewed-by: Matt Coster <matt.coster@imgtec.com>
Tested-by: Nathan Chancellor <nathan@kernel.org> # build
Link: https://patchwork.freedesktop.org/patch/msgid/190e4eefef6c5e62052a01af0084c69361e216ef.1725962479.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/imagination/pvr_drv.c

@@ -220,7 +220,7 @@ err_drm_dev_exit:
 	return ret;
 }
 
-static __always_inline u64
+static __always_inline __maybe_unused u64
 pvr_fw_version_packed(u32 major, u32 minor)
 {
 	return ((u64)major << 32) | minor;