drm/i915: vlv: fix save/restore of GFX_MAX_REQ_COUNT reg

Due this typo we don't save/restore the GFX_MAX_REQ_COUNT register across
suspend/resume, so fix this.

This was introduced in

commit ddeea5b0
Author: Imre Deak <imre.deak@intel.com>
Date:   Mon May 5 15:19:56 2014 +0300

    drm/i915: vlv: add runtime PM support

I noticed this only by reading the code. To my knowledge it shouldn't
cause any real problems at the moment, since the power well backing this
register remains on across a runtime s/r. This may change once
system-wide s0ix functionality is enabled in the kernel.

v2:
- resend after a missing git add -u :/

Cc: stable@vger.kernel.org
Signed-off-by: Imre Deak <imre.deak@intel.com>
Tested-By: PRC QA PRTS (Patch Regression Test System Contact: <shuang.he@intel.com)>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>