jlink: deconflict local variables from global symbols

jlink: deconflict local variables from global symbols

BeagleBone debian 7 builds produce:
    jlink.c: In function 'jlink_speed':
    jlink.c:218:11: error: declaration of 'div' shadows a global declaration [-Werror=shadow]
    jlink.c: In function 'check_trace_freq':
    jlink.c:1065:54: error: declaration of 'div' shadows a global declaration [-Werror=shadow]
    jlink.c: In function 'config_trace':
    jlink.c:1101:11: error: declaration of 'div' shadows a global declaration [-Werror=shadow]

Fix this by changing the local variable to 'divider'.

Change-Id: I96a0cc0f7d4d4af5a56aa1e918e5416d3c61cbfe
Signed-off-by: Peter A. Bigot <pab@pabigot.com>
Reviewed-on: http://openocd.zylin.com/3185
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>