Dropping PREFIX from the building make caused regression in runtime path resolution

Description:

8532d531 removes the explicit PREFIX from the building make but apparently there's no default and it controls the DATA_DIR, https://github.com/rvaiya/keyd/blob/7c0aecb8bfd34dc8642bf4eefd2e59c89e61cec3/Makefile#L20 what leads to a regression of runtime resolution for relative paths.

Additional info:

• package version(s): 2.6.0-1
• link to upstream bug report: https://github.com/rvaiya/keyd/issues/1189 https://bbs.archlinux.org/viewtopic.php?id=311377

Steps to reproduce:

1. Try to include a relative path in /etc/keyd/keyd.conf
2. Get an error