common/cmd_ide.c: fix GCC 4.6 build warnings

Fix:
cmd_ide.c: In function 'ide_ident':
cmd_ide.c:988:6: warning: variable 'do_retry' set but not used
[-Wunused-but-set-variable]

Delete the unused variable.

Signed-off-by: Wolfgang Denk <wd@denx.de>