msm: kgsl: Remove incorrect check for current context

We remove an incorrect check for currently active context.
The intent of the original check was to ensure that the
current context is at least there/valid before we issue
a dummy command with a forced interrupt. However, this
check was implemented incorrectly, instead of checking
the context under which the function is running, the check
was probing the "drawctxt_active" which may not necessarily
be the same as the context for which the function was called.
We fix this by changing the check to instead look for the
context under which the kgsl_check_interrupt_timestamp() has
been called.

CRs-fixed: 426186
Change-Id: I6ac123d16888287b14e6e53028f482eb709f24c5
Signed-off-by: Harsh Vardhan Dwivedi <hdwivedi@codeaurora.org>