arm: mach-omap2: smartreflex: fix another memory leak

Temporary strings with volt_* file names should be released after the
debugfs entries are created. While at it, also simplify the string
allocation, and use just snprintf() to create the name.

The patch eliminates kmemleak reports with the following stack trace
(multiple objects depending on HW):

unreferenced object 0xcedbc5a0 (size 64):
  comm "swapper", pid 1, jiffies 4294929375 (age 423.734s)
  hex dump (first 32 bytes):
    76 6f 6c 74 5f 39 37 35 30 30 30 00 00 00 00 00  volt_975000.....
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<c012fee0>] create_object+0x104/0x208
    [<c012dbc8>] kmem_cache_alloc_trace+0xf0/0x17c
    [<c0013f64>] omap_sr_probe+0x314/0x420
    [<c02a1724>] platform_drv_probe+0x18/0x1c
    [<c02a088c>] driver_probe_device+0xc8/0x188
    [<c02a09b4>] __driver_attach+0x68/0x8c
    [<c02a00ac>] bus_for_each_dev+0x44/0x74
    [<c029f9e0>] bus_add_driver+0xa0/0x228
    [<c02a0cac>] driver_register+0xa8/0x130
    [<c02a1b2c>] platform_driver_probe+0x18/0x8c
    [<c0013c1c>] sr_init+0x40/0x74
    [<c005a554>] do_one_initcall+0xc8/0x1a0
    [<c00084f4>] kernel_init+0x150/0x218
    [<c0065d64>] kernel_thread_exit+0x0/0x8
    [<ffffffff>] 0xffffffff

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>