libpayload: Make the source for lzma decompression const

Change-Id: I9a16331dedc97f17af94bf2cf535a9c93d1729a0
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: http://review.coreboot.org/2667
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

payloads/libpayload/include/lzma.h

@@ -35,6 +35,6 @@
  *
  * returns the decompressed size, or 0 on error
  */
-unsigned long ulzma(unsigned char *src, unsigned char *dst);
+unsigned long ulzma(const unsigned char *src, unsigned char *dst);
 
 #endif