cpufreq: qcom: fix writes in read-only memory region

In the Linux kernel, the following vulnerability has been resolved:

cpufreq: qcom: fix writes in read-only memory region

This commit fixes a kernel oops because of a write in some read-only memory:

[ 9.068287] Unable to handle kernel write to read-only memory at virtual address ffff800009240ad8

..snip..

[ 9.138790] Internal error: Oops: 9600004f [#1] PREEMPT SMP

..snip..

[ 9.269161] Call trace:

[ 9.276271] __memcpy+0x5c/0x230

[ 9.278531] snprintf+0x58/0x80

[ 9.282002] qcom_cpufreq_msm8939_name_version+0xb4/0x190

[ 9.284869] qcom_cpufreq_probe+0xc8/0x39c

..snip..

The following line defines a pointer that point to a char buffer stored

in read-only memory:

char *pvs_name = "speedXX-pvsXX-vXX";

This pointer is meant to hold a template "speedXX-pvsXX-vXX" where the

XX values get overridden by the qcom_cpufreq_krait_name_version function. Since

the template is actually stored in read-only memory, when the function

executes the following call we get an oops:

snprintf(*pvs_name, sizeof("speedXX-pvsXX-vXX"), "speed%d-pvs%d-v%d",

speed, pvs, pvs_ver);

To fix this issue, we instead store the template name onto the stack by

using the following syntax:

char pvs_name_buffer[] = "speedXX-pvsXX-vXX";

Because the `pvs_name` needs to be able to be assigned to NULL, the

template buffer is stored in the pvs_name_buffer and not under the

pvs_name variable.