OMAP4: clock: Remove clock hacks from timer-gp.c

Now the omap4 clock framework is in mainline and clk_get_rate()
is functional. Hence reomve the hardcoded clock hacks.

This patch also fixes
Division by zero in kernel.
Backtrace:
[<c0025fb8>] (dump_backtrace+0x0/0x110) from [<c017febc>] (dump_stack+0x18/0x1c)
 r7:60000093 r6:c0641050 r5:c0223e78 r4:c02126b4
[<c017fea4>] (dump_stack+0x0/0x1c) from [<c00260fc>] (__div0+0x18/0x20)
[<c00260e4>] (__div0+0x0/0x20) from [<c01431fc>] (Ldiv0+0x8/0x10)
[<c00318d4>] (omap_dm_timer_stop+0x0/0xb0) from [<c002c148>] (omap2_gp_timer_set_mode+0x1c/0x68)
 r5:c0223e78 r4:00000000
[<c002c12c>] (omap2_gp_timer_set_mode+0x0/0x68) from [<c0063270>] (clockevents_set_mode+0x30/0x64)
 r5:c020cae0 r4:00000000
[<c0063240>] (clockevents_set_mode+0x0/0x64) from [<c00632fc>] (clockevents_exchange_device+0x30/0x9c)
 r5:c020cae0 r4:c02146e0
[<c00632cc>] (clockevents_exchange_device+0x0/0x9c) from [<c00636e0>] (tick_notify+0x17c/0x404)
 r7:00000000 r6:c0641050 r5:00000000 r4:c020cae0
[<c0063564>] (tick_notify+0x0/0x404) from [<c005d5fc>] (notifier_call_chain+0x34/0x78)
[<c005d5c8>] (notifier_call_chain+0x0/0x78) from [<c005d684>] (__raw_notifier_call_chain+0x1c/0x24)
[<c005d668>] (__raw_notifier_call_chain+0x0/0x24) from [<c005d6ac>] (raw_notifier_call_chain+0x20/0x28)
[<c005d68c>] (raw_notifier_call_chain+0x0/0x28) from [<c0062e78>] (clockevents_do_notify+0x1c/0x24)
[<c0062e5c>] (clockevents_do_notify+0x0/0x24) from [<c0062f18>] (clockevents_register_device+0x98/0xd0)
[<c0062e80>] (clockevents_register_device+0x0/0xd0) from [<c001a194>] (percpu_timer_setup+0x80/0x9c)
 r7:00000000 r6:00000002 r5:00000002 r4:00000003
[<c001a114>] (percpu_timer_setup+0x0/0x9c) from [<c000e9f0>] (smp_prepare_cpus+0xb0/0xe8)
[<c000e940>] (smp_prepare_cpus+0x0/0xe8) from [<c00084e8>] (kernel_init+0x5c/0x1fc)
 r7:00000000 r6:00000000 r5:00000000 r4:c001b8a4
[<c000848c>] (kernel_init+0x0/0x1fc) from [<c0046c50>] (do_exit+0x0/0x604)
 r7:00000000 r6:00000000 r5:00000000 r4:00000000

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>