msm: board-msm7627a-wlan: Handle gpio request failures properly

Target freeze is observed when AR600x wlan driver is loaded
on 7x27a FFA platform which has WCN chipset in it.

msm_AR600X_setup_power() func already takes care of disabling
regulator setting in gpio request (WLAN_DEEP_SLEEP_N) failure
cases. msm_AR600X_shutdown_power() func should NOT try to disable
any regulator related setting when there is gpio request
failures. Doing that in msm_AR600X_shutdown_power() will
lead to the target freeze.

This patch modifies msm_AR600X_shutdown_power() not to perform
any regulator setting in case of gpio request failures.

Change-Id: Iec4737d7c1479fba9d644cc01e38ff3c1ffa02b2
Signed-off-by: Ming-yi Lin <mylin@codeaurora.org>