obmc-phosphor-discovery-service: fix bitbake warning

Fix the following warning in bitbake:
    WARNING: python should use 4 spaces indentation, but found tabs in
    obmc-phosphor-discovery-service.bbclass, line 76

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I389b9b2e2041ad3ad68c788292cb85adec564d3d
diff --git a/classes/obmc-phosphor-discovery-service.bbclass b/classes/obmc-phosphor-discovery-service.bbclass
index fdade60..48760f3 100644
--- a/classes/obmc-phosphor-discovery-service.bbclass
+++ b/classes/obmc-phosphor-discovery-service.bbclass
@@ -73,7 +73,7 @@
             fd.write('<!DOCTYPE service-group SYSTEM "avahi-service.dtd">\n')
             fd.write('<service-group>\n')
             fd.write('        <name replace-wildcards="yes">%s on %%h</name>\n'
-			    % service_name)
+                % service_name)
             fd.write('        <service>\n')
             fd.write('                <type>%s</type>\n' % service_type)
             fd.write('                <port>%s</port>\n' % service_port)