ARM: OMAP: Fix sleep under spinlock for cpufreq

[   10.523437] BUG: sleeping function called from invalid context at kernel/mut6
[   10.523437] in_atomic():0, irqs_disabled():128
[   10.523437] [<c002c168>] (dump_stack+0x0/0x14) from [<c005374c>] (__might_sl)
[   10.523437] [<c0053698>] (__might_sleep+0x0/0xd4) from [<c024fdf4>] (mutex_l)
[   10.523437]  r5 = C02F0DE8  r4 = C02F0DF0
[   10.523437] [<c024fdd4>] (mutex_lock+0x0/0x44) from [<c0041df4>] (clk_get+0x)
[   10.523437]  r4 = 00000000
[   10.523437] [<c0041da4>] (clk_get+0x0/0x128) from [<c0046520>] (omap_getspee)
[   10.523437]  r8 = 00000002  r7 = 00000000  r6 = C031DAF8  r5 = C0473980
[   10.523437]  r4 = 00000000
[   10.523437] [<c00464fc>] (omap_getspeed+0x0/0x5c) from [<c01b8518>] (cpufreq)
[   10.523437]  r5 = C0473980  r4 = 00000002

Signed-off-by: Hiroshi DOYU <Hiroshi.DOYU@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>