tools: Fix hex2hcd compilation error
tools: Fix hex2hcd compilation error

Fix following with GCC version 4.8.2 (Debian 4.8.2-21):

tools/hex2hcd.c: In function ‘main’:
tools/hex2hcd.c:118:19: error: comparison between signed and
  unsigned integer expressions [-Werror=sign-compare]
     for (i = 0; i < hex_to_int(rbuf + 1); i++) {
                   ^
cc1: all warnings being treated as errors

mapfau/bluez,ComputeCycles/bluez,silent-snowman/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,pkarasev3/bluez,mapfau/bluez,mapfau/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,mapfau/bluez,ComputeCycles/bluez,pkarasev3/bluez,pkarasev3/bluez