Fix: ppdLutLoad() returning NULL due to undersized spec buffer

[rkt0209]

Problem

ppdLutLoad() in ppd/ppd-load-profile.c declares its spec[] buffer as PPD_MAX_NAME (41 bytes), then passes that buffer to ppdFindColorAttr(). But ppdFindColorAttr()
rejects any caller whose specsize < IPP_MAX_NAME (256 bytes):

// ppd/ppd-load-profile.c (current master), lines 55-57
if (!ppd || !name || !colormodel || !media || !resolution || !spec ||
    specsize < IPP_MAX_NAME)
  return (NULL);

As a result, every call to ppdLutLoad() returns NULL — the function is effectively dead code on master. Any printer driver that relies on cups*Dither /
cupsAllDither PPD attributes for halftone LUT loading silently gets no LUT.

The sibling functions in the same file (ppdRGBLoad() at line 193, ppdCMYKLoad() at line 311) already declare their spec[] buffer as IPP_MAX_NAME, so this is clearly an
oversight in ppdLutLoad() alone.

Fix

Change one character — make ppdLutLoad's spec buffer IPP_MAX_NAME to match what ppdFindColorAttr() requires.

   char               name[PPD_MAX_NAME],     // Attribute name
-             spec[PPD_MAX_NAME];     // Attribute spec
+             spec[IPP_MAX_NAME];     // Attribute spec

No API change, no behaviour change for callers that were already getting NULL — they now get the LUT the function was always meant to return.