Stop temporarily storing a pointer to a constant literal string
in a char *, just to strdup it a few lines later.

Fixes gcc -Wwrite-strings warnings:

xkbInit.c: In function 'XkbGetRulesDflts':
xkbInit.c:121:38: warning: assignment discards qualifiers from pointer target type
xkbInit.c:123:23: warning: assignment discards qualifiers from pointer target type
xkbInit.c:125:24: warning: assignment discards qualifiers from pointer target type
xkbInit.c:127:25: warning: assignment discards qualifiers from pointer target type
xkbInit.c:129:25: warning: assignment discards qualifiers from pointer target type

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>