decompress_unlzma: make "fast" version a bit smaller

It is not slower. In fact it seems a tiny bit faster too.

   text	   data	    bss	    dec	    hex	filename
   2827	      0	      0	   2827	    b0b	decompress_unlzma.o
   2797	      0	      0	   2797	    aed	decompress_unlzma.o

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
decompress_unlzma: 10% speedup in "small" code

   text	   data	    bss	    dec	    hex	filename
   1796	      0	      0	   1796	    704	decompress_unlzma.o
   1801	      0	      0	   1801	    709	decompress_unlzma.o

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
decompress_unlzma: move function, no code changes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Merge git://busybox.net/busybox