env: correct sign for error code

Error codes should be negative.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/common/env_attr.c b/common/env_attr.c
index 5bfe5e3..3862190 100644
--- a/common/env_attr.c
+++ b/common/env_attr.c
@@ -153,7 +153,7 @@
 		}
 	} else {
 		printf("Error compiling regex: %s\n", slre.err_str);
-		retval = EINVAL;
+		retval = -EINVAL;
 	}
 done:
 	return retval;