clean up symbol export regex

Co-authored-by: Miguel Ojeda <ojeda@users.noreply.github.com>

Author: adamrk

rust/Makefile

@@ -72,7 +72,7 @@ $(objtree)/rust/bindings_generated.rs: $(srctree)/rust/kernel/bindings_helper.h
 quiet_cmd_exports = EXPORTS $@
       cmd_exports = \
 	$(NM) -p --defined-only $< \
-		| grep -E '( T | R )' | cut -d ' ' -f 3 | grep -E '^(__rust_|_R)' \
+		| grep -E ' (T|R) ' | cut -d ' ' -f 3 | grep -E '^(__rust_|_R)' \
 		| xargs -n1 -Isymbol \
 		echo 'EXPORT_SYMBOL$(exports_target_type)(symbol);' > $@