[PATCH] fbdev: Reduce stack usage

calc_mode_timings() and fb_get_mode() are using more than 500 bytes off the
stack.  Fix.

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>