intel/compiler: don't use a keyword struct for a class fs_reg

warning: struct 'fs_reg' was previously declared as a class
Fixes: e64be391 ("intel/compiler: generalize the combine constants pass")
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Andrii Simiklit <andrii.simiklit@globallogic.com>

src/intel/compiler/brw_fs_combine_constants.cpp

@@ -289,7 +289,7 @@ get_alignment_for_imm(const struct imm *imm)
 }
 
 static bool
-needs_negate(const struct fs_reg *reg, const struct imm *imm)
+needs_negate(const fs_reg *reg, const struct imm *imm)
 {
    switch (reg->type) {
    case BRW_REGISTER_TYPE_DF: