getfattr: fix "getfattr NOTEXIST" - now prints error msg

function                                             old     new   delta
getfattr_main                                        309     307      -2
.rodata                                           105395  105391      -4
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(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-6)               Total: -6 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>